Working through final wiring issues on my build and I'm stumped

sab said:
If I was frustrated by people doing their best to broaden their knowledge, I wouldn't have participated in this thread. I've had some awesome mentors, starting with my father, and maintaining vehicles is a dying activity. I like doing what I can to keep that spirit alive!


I can't tell from the picture, but looking at the pin out for C154, that section of the harness should have three of or four (more on that next) wires in it - one or two Black wires, one Violet with Black Stripe wire, and one Violet with White Stripe wire. Here's that pin out from the FSM:
View attachment 536143
I'm with you - if the black wire was broken, splicing it should have fixed you issue. The black wire is in the ground path for starter relay coil.

Side note - it seems that everywhere you turn, you're finding problems with that TJ. You've got your work cut out for you!


That's still seems like too much resistance to me.


I looked into that a bit yesterday. Go back up and look at the C154 pin out above. Notice that, for a manual transmission, both pin 1 and pin 3 are the BK wire. I believe that you'll find that one of them goes to G105, and the other goes to the other pin - like a Daisy Chain. That said, I have no way of determining why that is. I also have no way to tell what happens if that jumper (between Pin 1 and Pin 3) is broken. Test resistance from Pin 1 to G105 and then again from Pin 3 and G105. Also do it for Pin 1 to Pin 3. Report back with results.

In addition, you should pull all of the wiring from C154 to the break you repaired out of the loom and inspect it. Is there a short black jumper wire between Pin 1 and Pin 3?


S134 is a splice, not a connector. Harness section #3 goes from the PDC's starter relay socket to Connector C104. Splice S134 is located here:
View attachment 536151


Keep doing the yeoman's work. First, let's make sure your meter leads aren't finky. What's the resistance when you touch the red probe to the black probe? It should be 0.1 or 0.0, depending on the meter. If it's higher than that, we have problems.

Second, my suggestion is pull everything out of the looms to inspect it. Compare wire colors to a study of the wiring schematics. The way the schematics work, it's not easy to do that because there is no actual diagram of the wiring harness. You're looking to confirm that no one has screwed with the harness and for obvious damage, like that broken wire you found. Then you can use the resistance measurements to try to pin-point the source of the high resistance. Everything should be a dead short, or 0.1 ohms. Anything higher than that means something is wrong.
Click to expand...

Thank you again!

Okay, staying positive. I'm going to slow this down and do it right. One step at a time. Starting from the beginning. G105 to C154.

G105: I took both eye rings off, sanded both sides of both, sanded the nut and the bolt, and reassembled.

C154: I de-loomed everything from G105 to C154. I can confirm that the broken wire only had one place it could go. It was the black wire coming out of the connector, and it went to the broken black wire in the loom. The other three wires are in good shape. Those are violet/white, violet/black, brown/light blue. Those wires are all connected correctly (I'll add pictures to this post once I post, as I edit and add pictures from my phone).

I checked every inch of the black wires and the brown/light blue wires from G105 to C154. I cannot find any break of any kind. I think I see S132 (the splice of ground wires in the picture). That all looks good too.

I touched the leads of the multimeter together and got a 0.00 reading.

I used a jumper wire pushed into the pin with the black wire in C154 and ran it up a lead from my multimeter. I ran other other lead to the ground bolt at G105. The multimeter read 0.4 ohms when on the 200 setting.

I'll stop there for now and see your thoughts so I don't get ahead of myself with any next steps. If that is too much resistance, I'm not sure what is wrong because I can't find any issues with the ground wire between the two points.

Side note: There seem to be so many inconsistencies in the FSM. It has the brown/light blue wire listed as an auto trans wire. But that's been labeled as the manual trans wire elsewhere, and you can see in my harness it's there. This was a manual trans Jeep from factory.... So strange.

IMG_6629.jpeg


IMG_6630.jpeg


IMG_6631.jpeg


IMG_6632.jpeg
 
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I'm trying to get out of the office and home, so for now, I'll just share some random thoughts, in no particular order, and with no proof-reading (I always find errors in my first draft). After dinner, I'll mull some more and try to respond with more purpose. My thoughts:
  1. Your multimeter leads are fine (0.00 ohms), so we can eliminate that.
  2. If you look at the ground path in the schematic, you'll see that there is a number above the wire color. That's the wire gauge for that section of wire. Sections 2 and 3 that I marked in read are 20 gauge, and Section one is 20 gauge from C154 to S132, and then 14 gauge from there to G105. Let's do a little thought experiment. Let's assume it's all 20 gauge, being conservative. For every foot of 20 gauge wire, you'll get 0.01 ohms. So, if you are seeing 0.40 ohms, that would be about 40 feet of wire. Is there 40 feet of wire between G105 and C154? No. That's why that's an important observation. It means something is causing excessive resistance. That's almost always a bad connection.
  3. Let's count all the connections (any one, or combination thereof, could be a source of increased resistance) from battery negative to the relay coil, starting at the battery:
    1. Battery post to cable lug
    2. Cable lug to cable
    3. Cable to G107 ring eye
    4. G107 ring eye to G105 ring eye
    5. G105 ring eye to wire
    6. Wire to S132 splice
    7. S132 splice to next wire
    8. Wire to C154 connector terminal
    9. C154 connector #1 terminal to "Manual Transmission Jumper Wire" (still wondering about that since you appear to have an oddity with the BR/LB wire on Pin 3 instead of another BK wire)
    10. "Manual Transmission Jumper Wire" to C154 connector #3 terminal
    11. C154 connector #3 terminal to wire
    12. Wire to S134 splice
    13. S134 splice to wire
    14. Wire to C104 connector Pin 5 terminal
    15. C104 connector Pin 5 mating terminal
    16. C104 connector Pin 5 mating terminal to wire
    17. Wire to Starter Relay Coil D13 terminal at PDC
  4. You still should cut the black wire you spliced and put your ground jumper back in to see if the TJ starts. I don't think you've owned this TJ since new, so someone may have purposely cut that wire to solve a problem caused by a modification previously. If cutting and jumping works again, we know somethings been poorly modified and we have our work cut out for us...
  5. Can you take a picture of C154 showing the wires coming out the back?
 
So, it’s well after dinner now, and I’ve been mulling. I’ve got nothing new to contribute, so I’ll sleep on it…
 
sab said:
I'm trying to get out of the office and home, so for now, I'll just share some random thoughts, in no particular order, and with no proof-reading (I always find errors in my first draft). After dinner, I'll mull some more and try to respond with more purpose. My thoughts:
  1. Your multimeter leads are fine (0.00 ohms), so we can eliminate that.
  2. If you look at the ground path in the schematic, you'll see that there is a number above the wire color. That's the wire gauge for that section of wire. Sections 2 and 3 that I marked in read are 20 gauge, and Section one is 20 gauge from C154 to S132, and then 14 gauge from there to G105. Let's do a little thought experiment. Let's assume it's all 20 gauge, being conservative. For every foot of 20 gauge wire, you'll get 0.01 ohms. So, if you are seeing 0.40 ohms, that would be about 40 feet of wire. Is there 40 feet of wire between G105 and C154? No. That's why that's an important observation. It means something is causing excessive resistance. That's almost always a bad connection.
  3. Let's count all the connections (any one, or combination thereof, could be a source of increased resistance) from battery negative to the relay coil, starting at the battery:
    1. Battery post to cable lug
    2. Cable lug to cable
    3. Cable to G107 ring eye
    4. G107 ring eye to G105 ring eye
    5. G105 ring eye to wire
    6. Wire to S132 splice
    7. S132 splice to next wire
    8. Wire to C154 connector terminal
    9. C154 connector #1 terminal to "Manual Transmission Jumper Wire" (still wondering about that since you appear to have an oddity with the BR/LB wire on Pin 3 instead of another BK wire)
    10. "Manual Transmission Jumper Wire" to C154 connector #3 terminal
    11. C154 connector #3 terminal to wire
    12. Wire to S134 splice
    13. S134 splice to wire
    14. Wire to C104 connector Pin 5 terminal
    15. C104 connector Pin 5 mating terminal
    16. C104 connector Pin 5 mating terminal to wire
    17. Wire to Starter Relay Coil D13 terminal at PDC
  4. You still should cut the black wire you spliced and put your ground jumper back in to see if the TJ starts. I don't think you've owned this TJ since new, so someone may have purposely cut that wire to solve a problem caused by a modification previously. If cutting and jumping works again, we know somethings been poorly modified and we have our work cut out for us...
  5. Can you take a picture of C154 showing the wires coming out the back?
Click to expand...

Thanks for all the thoughts.

I have added a picture I just took of the back of the harness with the connector removed again. I plugged the harness back in and tried jumping it from the relay to the negative post of the battery like before. Still no start or crank. The only other things I can see are different now from when it worked previously is that I removed the extra ground cable from G105/107 to the frame. Everything else was simply unplugged and plugged back in.

IMG_6653.jpeg
 
sab said:
I'm trying to get out of the office and home, so for now, I'll just share some random thoughts, in no particular order, and with no proof-reading (I always find errors in my first draft). After dinner, I'll mull some more and try to respond with more purpose. My thoughts:
  1. Your multimeter leads are fine (0.00 ohms), so we can eliminate that.
  2. If you look at the ground path in the schematic, you'll see that there is a number above the wire color. That's the wire gauge for that section of wire. Sections 2 and 3 that I marked in read are 20 gauge, and Section one is 20 gauge from C154 to S132, and then 14 gauge from there to G105. Let's do a little thought experiment. Let's assume it's all 20 gauge, being conservative. For every foot of 20 gauge wire, you'll get 0.01 ohms. So, if you are seeing 0.40 ohms, that would be about 40 feet of wire. Is there 40 feet of wire between G105 and C154? No. That's why that's an important observation. It means something is causing excessive resistance. That's almost always a bad connection.
  3. Let's count all the connections (any one, or combination thereof, could be a source of increased resistance) from battery negative to the relay coil, starting at the battery:
    1. Battery post to cable lug
    2. Cable lug to cable
    3. Cable to G107 ring eye
    4. G107 ring eye to G105 ring eye
    5. G105 ring eye to wire
    6. Wire to S132 splice
    7. S132 splice to next wire
    8. Wire to C154 connector terminal
    9. C154 connector #1 terminal to "Manual Transmission Jumper Wire" (still wondering about that since you appear to have an oddity with the BR/LB wire on Pin 3 instead of another BK wire)
    10. "Manual Transmission Jumper Wire" to C154 connector #3 terminal
    11. C154 connector #3 terminal to wire
    12. Wire to S134 splice
    13. S134 splice to wire
    14. Wire to C104 connector Pin 5 terminal
    15. C104 connector Pin 5 mating terminal
    16. C104 connector Pin 5 mating terminal to wire
    17. Wire to Starter Relay Coil D13 terminal at PDC
  4. You still should cut the black wire you spliced and put your ground jumper back in to see if the TJ starts. I don't think you've owned this TJ since new, so someone may have purposely cut that wire to solve a problem caused by a modification previously. If cutting and jumping works again, we know somethings been poorly modified and we have our work cut out for us...
  5. Can you take a picture of C154 showing the wires coming out the back?
Click to expand...

Last night before I left the house for a bit (went and walked the beach a bit to let some of the stress of this Jeep go), I checked the next sections of wiring just to see what I would get. I know it may not align exactly to where you break it down with your 3 sections, but the first one showed 0.4 ohms as I mentioned above. For the next section of wiring I did the BR/LB wire coming out of C154 up to the gray wiring connecter above the engine (I don't know which connecter number it is). It comes up the firewall (via the bundle of wires), into this connector, through the connector and over to the PCM before going to the PDC. The resistance for the BR/LB wire from C154 to the gray connector is 0.4 ohms. The resistance from the other side of that same gray connector to the wire terminal in the back of the PDC is also 0,4 ohms.

Getting the exact same reading each step makes me feel like I have no idea what I'm doing and that I am making quite a confusing mess out of this.
 
OK, your posts give me some fresh ideas to try:
  1. Put the frame to engine ground strap back, put your jumper back in, and see if it starts again. As you know, getting back to where the jumper worked would be helpful and give valuable information.
  2. Trace each of those wires from C154 back to their other ends. From your last post above this one, you've traced the BR/LB wire from C154 to what should be C104 and on to the PDC. You should have encountered S134 in between. Did you see this splice? You should be constantly referring to Sec. 8W in the FSM because it shows the locations of all grounds, splices, and connectors, and you need to verify that all of these wire paths are unmolested by previous owners. Trace the other three wires in C154 and compare to 8W locations and schematics. We need to figure out how you got 0.7 ohms from G105 to the PDC with that black wire broken. It should have been an open circuit. That's a key piece of information.
  3. I thought there'd be a jumper wire between Pins 1 and 3 on the back side of C154 (the "Manual Transmission Jumper"). If it's not there, it must be on the other side of the mating connector. Please measure resistance across Pins 1 and 3 on the mating connector (FYI: In your picture above, Pin 4 is on the left and Pin 1 is on the right). If I'm right, it should be continuity, so 0.1 ohms. If that jumper is messed up, it could be a problem (I'm not going to say "the" problem anymore - 'cuz you have seem to have multiple! :()
Gormy said:
Getting the exact same reading each step makes me feel like I have no idea what I'm doing and that I am making quite a confusing mess out of this.
Click to expand...
Actually, this may make sense. Resistance is additive, and you're working at the low end of your multimeter's resistance-measuring capability. Last night, you got 0.4 ohms for what I called Section 2 from C154 to what I think is C104 (check the FSM for that connector location to confirm, please), and you got 0.4 ohms from C104 to the PDC (what I called Section 3). What resistance do you now get from the PDC relay coil connector to Batt Neg? If it's greater than the sum of those two 0.4 ohm readings, you're still on the right path. Also, keep in mind that measuring with multimeter probes can induce some resistance in the probe-to-wire or probe-to-connector connection. Very solid pressure on the probe handle can minimize this. A limp-wristed probe can add resistance, or result in a varying reading.

Also, did you get 0.76 ohms from Batt Neg to G107, too? Please confirm.

At this point, you have to systematically measure each section's resistance, and then go after each of the connections I noted in Post 83. Also, the splice @mrblaine mentioned should just be replaced, since it's a known problem. You simply cannot tell that a connection is good just by looking at it. You just have to believe me there. Been there, done that. At this point, you are on the proverbial wild goose chase, and you will end up doing a lot of things that don't solve the problem, but they need to be done to firmly eliminate possibilities...

So, let me summarize key points:
  1. You have to trace all the wires and compare to the wiring schematic because someone has messed with this TJ's wiring. Trust nothing.
  2. Use your ohmmeter to systematically check the ground path connections. This will lead you to the offending connection(s) (the one or more with R>0.1 ohms). The way I usually do this is by using what I call the "rule of halves." If you have seventeen connections to check, start by checking resistance from #1 to #8 (in path order, of course). Then check from #9 to #17. Hopefully, one of those will be 0.1 ohms and the other higher. That tells you which half to concentrate on next. Let's say that happens to be the #1 to #8 path. So now, check from #1 to #4 and then from #5 to #8. And so on. By cutting (not literally!) each path in half, you more quickly find the offending connection. However, on old vehicles, made with poor-quality wiring harness components, and driven in less-than-ideal environmental conditions (your TJ), this doesn't always work because many connections are bad. In that case, you just have to replace section(s) of harness. Not fun, but do-able.
Keep your chin up! It's a man-made vehicle, which means it's fixable. You just have to persevere!
 
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sab said:
OK, your posts give me some fresh ideas to try:
  1. Put the frame to engine ground strap back, put your jumper back in, and see if it starts again. As you know, getting back to where the jumper worked would be helpful and give valuable information.
  2. Trace each of those wires from C154 back to their other ends. From your last post above this one, you've traced the BR/LB wire from C154 to what should be C104 and on to the PDC. You should have encountered S134 in between. Did you see this splice? You should be constantly referring to Sec. 8W in the FSM because it shows the locations of all grounds, splices, and connectors, and you need to verify that all of these wire paths are unmolested by previous owners. Trace the other three wires in C154 and compare to 8W locations and schematics. We need to figure out how you got 0.7 ohms from G105 to the PDC with that black wire broken. It should have been an open circuit. That's a key piece of information.
  3. I thought there'd be a jumper wire between Pins 1 and 3 on the back side of C154 (the "Manual Transmission Jumper"). If it's not there, it must be on the other side of the mating connector. Please measure resistance across Pins 1 and 3 on the mating connector (FYI: In your picture above, Pin 4 is on the left and Pin 1 is on the right). If I'm right, it should be continuity, so 0.1 ohms. If that jumper is messed up, it could be a problem (I'm not going to say "the" problem anymore - 'cuz you have seem to have multiple! :()

Actually, this may make sense. Resistance is additive, and you're working at the low end of your multimeter's resistance-measuring capability. Last night, you got 0.4 ohms for what I called Section 2 from C154 to what I think is C104 (check the FSM for that connector location to confirm, please), and you got 0.4 ohms from C104 to the PDC (what I called Section 3). What resistance do you now get from the PDC relay coil connector to Batt Neg? If it's greater than the sum of those two 0.4 ohm readings, you're still on the right path. Also, keep in mind that measuring with multimeter probes can induce some resistance in the probe-to-wire or probe-to-connector connection. Very solid pressure on the probe handle can minimize this. A limp-wristed probe can add resistance, or result in a varying reading.

Also, did you get 0.76 ohms from Batt Neg to G107, too? Please confirm.

At this point, you have to systematically measure each section's resistance, and then go after each of the connections I noted in Post 83. Also, the splice @mrblaine mentioned should just be replaced, since it's a known problem. You simply cannot tell that a connection is good just by looking at it. You just have to believe me there. Been there, done that. At this point, you are on the proverbial wild goose chase, and you will end up doing a lot of things that don't solve the problem, but they need to be done to firmly eliminate possibilities...

So, let me summarize key points:
  1. You have to trace all the wires and compare to the wiring schematic because someone has messed with this TJ's wiring. Trust nothing.
  2. Use your ohmmeter to systematically check the ground path connections. This will lead you to the offending connection(s) (the one or more with R>0.1 ohms). The way I usually do this is by using what I call the "rule of halves." If you have seventeen connections to check, start by checking resistance from #1 to #8 (in path order, of course). Then check from #9 to #17. Hopefully, one of those will be 0.1 ohms and the other higher. That tells you which half to concentrate on next. Let's say that happens to be the #1 to #8 path. So now, check from #1 to #4 and then from #5 to #8. And so on. By cutting (not literally!) each path in half, you more quickly find the offending connection. However, on old vehicles, made with poor-quality wiring harness components, and driven in less-than-ideal environmental conditions (your TJ), this doesn't always work because many connections are bad. In that case, you just have to replace section(s) of harness. Not fun, but do-able.
Keep your chin up! It's a man-made vehicle, which means it's fixable. You just have to persevere!
Click to expand...

Sorry to reply in such small increments, but I’m squeezing quick tests in around work tasks. Just a quick run to the garage and then back upstairs to my desk. I reconnected the two black wire ends at C154 and tested resistance across pins 1 and 3. Looks like it could be an issue?

IMG_6654.jpeg
 
Following this. This fascinates me and worries me at the same time if I ever have to deal with it. Praying for that "haha" moment.

Is this frayed wiring from post #77? Or just part of the covering?

IMG_1536.jpeg
 
TokenJo said:
Following this. This fascinates me and worries me at the same time if I ever have to deal with it. Praying for that "haha" moment.

Is this frayed wiring from post #77? Or just part of the covering?

View attachment 536315
Click to expand...

That is frayed wire. It's the black wire in the back of the C154 connector by the transmission. As you read further you'll see pictures of the two ends of the black wire in one of my most recent pictures. I hoped reattaching that would solve all the issues. Sadly it did not.
 
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Gormy said:
I reconnected the two black wire ends at C154 and tested resistance across pins 1 and 3. Looks like it could be an issue?
Click to expand...
Ok, I think @JMT will appreciate this, and I need to give him credit because it was his posts some time ago that enlightened me ("semper discens!") I need to switch teaching methods from didactic to Socratic (readers, look it up - you'll learn something). I lean towards didactic, and most of this thread used that method.

Assuming the connector in your hand in the picture in Post 89 is the same as that in Post 86, why did you check resistance across Pins 1 and 3 after reconnecting the black wire? In other words, what were you trying to learn?
 
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sab said:
Ok, I think @JMT will appreciate this, and I need to give him credit because it was his posts some time ago that enlightened me ("semper discens!") I need to switch teaching methods from didactic to Socratic (readers, look it up - you'll learn something). I lean towards didactic, and most of this thread used that method.

Assuming the connector in your hand in the picture in Post 89 is the same as that in Post 86, why did you check resistance across Pins 1 and 3 after reconnecting the black wire? In other words, what were you trying to learn?
Click to expand...

I am probably misunderstanding your question because my mind is just spinning right now trying to take all this in, but I have a chance now to sit and type out what I did.

The connector in my hand in the picture in post 89 is indeed the same one as in post 86. I checked resistance across pins 1 and 3 after reconnecting the black wire to see if the connector was bad. The first reading that I have in the picture was high, but I cannot replicate it now. It now reads 0.4 like everything else. I had to check it with it connected because, from what I was guessing from looking at the wiring schematic with my limited experience, it looked like it just loops back to the wire harness from the transmission jumper (what I came to see as the harness with the two violet wires that goes into the side of the transmission). If the black wire is left broken, there is no complete circuit to test and it has no reading. The black wire needs to be attached.

I de-loomed the wires between the other end of the connector and the transmission jumper, and sure enough there is just a wire that loops it back to the harness. That's where it changes the wire color from black to BR/LB, an observation/question I made many, many posts back.

I then tested the resistance across pins 1 and 3 on the "engine side" of the connecter that goes back up to the main wire harness. Again, I get 0.4.

So now, with everything back in place, the black wire reconnected at C154, and testing every step of the wiring path (as close as I've explained so far for your 3 sections), as well as the full path with one lead on G105 on the engine block and the other lead at the BR/LB wire in he PDC, I have 0.4, or 40 ohms versus the 760 ohms that I started with. I believe fixing that black wire dropped it.

I'm guessing that is still too much? It is the same reading the whole way from the ground point onward. It still will not start, I have the NO BUS error still, and I can not start it by grounding the starter relay to the battery negative.

I will go back up to your longer post from yesterday as you left work and respond to those questions.

IMG_6655.jpeg


IMG_6656.jpeg
 
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I want to read through this whole thread again…we’re focusing a lot on ground. Has there been solid, indisputable proof that it’s possible to get the 12v pos signal to the starter solenoid?

A lot of times when solutions seem to get more and more complicated, I like to stop and reassess. Like you said, it was working once. It can’t be that far off.
 
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sab said:
OK, your posts give me some fresh ideas to try:
  1. Put the frame to engine ground strap back, put your jumper back in, and see if it starts again. As you know, getting back to where the jumper worked would be helpful and give valuable information.
Click to expand...
I did this as part of the testing I just did above. I should have checked if that changed the resistance reading before I did everything else, but I can go and pull the black wire apart at C154 again and see if I get a higher reading.
sab said:
  1. Trace each of those wires from C154 back to their other ends. From your last post above this one, you've traced the BR/LB wire from C154 to what should be C104 and on to the PDC. You should have encountered S134 in between. Did you see this splice? You should be constantly referring to Sec. 8W in the FSM because it shows the locations of all grounds, splices, and connectors, and you need to verify that all of these wire paths are unmolested by previous owners. Trace the other three wires in C154 and compare to 8W locations and schematics. We need to figure out how you got 0.7 ohms from G105 to the PDC with that black wire broken. It should have been an open circuit. That's a key piece of information.
Click to expand...
I believe I found it, yes. It should be the second picture in post 81. I will put more time into tracing all the specific wires, but I did not see any other issues. The black wire at C154 is what starts at G105. That goes to C154, through the harness, loops back around and back out the harness as BR/LB. This then goes up through S134 as you mentioned. I have traced this as far as I can and I have yet to find any issues with it. The other violet wires that go to the transmission jumper - I will have to trace those. I didn't focus on them as much as I was trying to find ground faults, so I was tracing the black wire and the BR/LB wire. I have no idea how it wasn't an open circuit and we still got a reading with that black wire broken. Maybe there was just one or two strands of wire still attached and when I pulled on the loom it tore it the rest of the way?
sab said:
  1. I thought there'd be a jumper wire between Pins 1 and 3 on the back side of C154 (the "Manual Transmission Jumper"). If it's not there, it must be on the other side of the mating connector. Please measure resistance across Pins 1 and 3 on the mating connector (FYI: In your picture above, Pin 4 is on the left and Pin 1 is on the right). If I'm right, it should be continuity, so 0.1 ohms. If that jumper is messed up, it could be a problem (I'm not going to say "the" problem anymore - 'cuz you have seem to have multiple! :()

Actually, this may make sense. Resistance is additive, and you're working at the low end of your multimeter's resistance-measuring capability. Last night, you got 0.4 ohms for what I called Section 2 from C154 to what I think is C104 (check the FSM for that connector location to confirm, please), and you got 0.4 ohms from C104 to the PDC (what I called Section 3). What resistance do you now get from the PDC relay coil connector to Batt Neg? If it's greater than the sum of those two 0.4 ohm readings, you're still on the right path. Also, keep in mind that measuring with multimeter probes can induce some resistance in the probe-to-wire or probe-to-connector connection. Very solid pressure on the probe handle can minimize this. A limp-wristed probe can add resistance, or result in a varying reading.
Click to expand...
I'm not sure I'm understanding the additive part of this. Are you saying it will build as it goes? So if section 1 had 0.4 and section 2 also had 0.4, are you saying that would then be 0.8? I'm not always starting over and testing G105 to the end points of each section. I'm starting from the beginning of each of your sections (where the previous one ended). Each is reading a 0.4. Then the entire thing from G105 to the PDC, it is a 0.4
sab said:
Also, did you get 0.76 ohms from Batt Neg to G107, too? Please confirm.
Click to expand...
I don't recall if I did that step yesterday. I feel like I've tested this 4,200 ways now.
sab said:
At this point, you have to systematically measure each section's resistance, and then go after each of the connections I noted in Post 83. Also, the splice @mrblaine mentioned should just be replaced, since it's a known problem. You simply cannot tell that a connection is good just by looking at it. You just have to believe me there. Been there, done that. At this point, you are on the proverbial wild goose chase, and you will end up doing a lot of things that don't solve the problem, but they need to be done to firmly eliminate possibilities...

So, let me summarize key points:
  1. You have to trace all the wires and compare to the wiring schematic because someone has messed with this TJ's wiring. Trust nothing.
  2. Use your ohmmeter to systematically check the ground path connections. This will lead you to the offending connection(s) (the one or more with R>0.1 ohms). The way I usually do this is by using what I call the "rule of halves." If you have seventeen connections to check, start by checking resistance from #1 to #8 (in path order, of course). Then check from #9 to #17. Hopefully, one of those will be 0.1 ohms and the other higher. That tells you which half to concentrate on next. Let's say that happens to be the #1 to #8 path. So now, check from #1 to #4 and then from #5 to #8. And so on. By cutting (not literally!) each path in half, you more quickly find the offending connection. However, on old vehicles, made with poor-quality wiring harness components, and driven in less-than-ideal environmental conditions (your TJ), this doesn't always work because many connections are bad. In that case, you just have to replace section(s) of harness. Not fun, but do-able.
Keep your chin up! It's a man-made vehicle, which means it's fixable. You just have to persevere!
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I know we're making good progress in narrowing it down, but I'm just feeling a little defeated right now. I know i created this mistake and I can't find it. The body tub and frame were from two separate vehicles, but the full drivetrain and wiring harness all came from the Jeep I bought. So I know this harness started this engine just fine as I started it myself; that's not just the word of a former owner. And the dash worked fine.
 
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Mike_H said:
I want to read through this whole thread again…we’re focusing a lot on ground. Has there been solid, indisputable proof that it’s possible to get the 12v pos signal to the starter solenoid?

A lot of times when solutions seem to get more and more complicated, I like to stop and reassess. Like you said, it was working once. It can’t be that far off.
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I did have power to the relay and starter solenoid, yes. Post 16 and 21 are where directions were given and my steps taken to ensure I had power to the relay. Then by grounding the relay to the negative post of the battery, posts 34 and 35, I could start it from the ignition.

I feel like it can't be anything real super deep. That's why I haven't gone tearing the ground splices apart yet. This worked in November, it was parked inside, the wiring harness wasn't in any elements, it was stripped off the old body, installed on the new body with the same drivetrain. I don't think anything too super hidden or deep into the harness should have broke. In my mind, it has to be a simple mistake I have made and am continuing to overlook.
 
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sab said:
Ok, I think @JMT will appreciate this, and I need to give him credit because it was his posts some time ago that enlightened me ("semper discens!") I need to switch teaching methods from didactic to Socratic (readers, look it up - you'll learn something). I lean towards didactic, and most of this thread used that method.

Assuming the connector in your hand in the picture in Post 89 is the same as that in Post 86, why did you check resistance across Pins 1 and 3 after reconnecting the black wire? In other words, what were you trying to learn?
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Meant to add this to an earlier reply, but instead of editing one of those and having it get lost if you already read it, I'll add it here.

If 40 ohms is too much resistance, and I have that right off the bat between the battery and G105, that seems like it would be the first issue, no? But from there, how does going from C154 also give me 40 ohms? And so does C105 to the PDC. It's consistently the same the entire way, no matter how far I go or where I start and finish. It's so odd.
 
I'm guessing .4 ohms is the "zero" on your meter. They all have plus or minuses of accuracy...the cheaper you go the worse they get. IMHO 40 nor 760 ohms of resistance should interrupt the ground path of the relay.

If you want yet another experiment to try you can run fresh, temporary wires and see if you get somewhere. But I think the ground issue is distracting us from another problem.

Single cause problems are easy enough to troubleshoot... it's the multiple problems stacked up culminating in a failure that are the doozies...hang in there and we'll (@sab) help you figure this out.

-Mac
 
Went and did one more test to try and rule things out before I let it sit for a bit and focus on work.

With the ground wire at C154 attached, I get a reading of 0.4 or 0.5 at the 200 setting, so 40-50 ohms. This reading is testing resistance from G105 to the BR/LB wire at the PDC.

With the ground wire at C154 not attached, I get a reading of 0.76 at the 20k setting, so 760 ohms. This reading is testing resistance from G105 to the BR/LB wire at the PDC.

I cannot get a reading with it attached at the 20k setting or not attached at the 200 setting, the dial has to be moved to get a reading. So to my untrained mind, that wire was clearly an issue, unfortunately not the only issue. However, I'm not certain from here why I cannot get it jumped by grounding it like I was doing before. It will still turn over and fire up just fine by jumping the starter to the battery.
 
macleanflood said:
I'm guessing .4 ohms is the "zero" on your meter. They all have plus or minuses of accuracy...the cheaper you go the worse they get.
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I had him touch probes together a few posts/pages back. That's how you eliminate "zero" issues. He got 0.00 ohms.

macleanflood said:
IMHO 40 nor 760 ohms of resistance should interrupt the ground path of the relay.
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This borders on categorically wrong. It's not flat-out wrong because I don't know what the relay coil resistance is. I had him measure it, but he got a very small value that would have resulted in hundreds of amps current. I then speculated that there could be a diode in parallel with the relay coil, which would affect the measurement (find that previous post if you want to know why). Keep in mind that any resistance in the ground path acts as a voltage divider. So, let's say that the relay coil is 40 ohms. Using Ohm's law, V=IxR, or I=V/R. At 12 V, I=12/40, or 0.3A. Now, put a 40 ohm resistor in parallel with the coil (a bad ground). I=V/R=12/(40+40)=0.15A. So the voltage at the relay coil is V=IxR=0.15 x 40=6V. The voltage is cut in half if the bad ground's resistance is equal to the coil resistance. Additionally, I previously pointed out that bad grounds often create resistance that increases with load. Think of the resistance as a bottle neck. Small amounts get through easily, but increase that flow more and more, and the effect becomes pronounced. Earlier, I pointed out that it is for this reason that some people prefer to use a test light because it puts more of a load on the circuit than a multimeter does.

macleanflood said:
If you want yet another experiment to try you can run fresh, temporary wires and see if you get somewhere. But I think the ground issue is distracting us from another problem.
Click to expand...
I've been trying to lead Gormy down a systematic path to determine root cause. This isn't helpful. He's run a ground bypass that was successful until it wasn't, so we're still trying to confirm or eliminate the ground as an issue. Unfortunately, it's complicated, and there appear to be multiple issues.

macleanflood said:
it's the multiple problems stacked up culminating in a failure that are the doozies...hang in there
Click to expand...
I agree 100%!

Mike_H said:
I want to read through this whole thread again…we’re focusing a lot on ground. Has there been solid, indisputable proof that it’s possible to get the 12v pos signal to the starter solenoid?

A lot of times when solutions seem to get more and more complicated, I like to stop and reassess. Like you said, it was working once. It can’t be that far off.
Click to expand...
Well, I've invested hours and hours into this, and I'm trying to systematically work through it. A fresh set of eyes on the thread makes very good sense, but let's please try to coordinate efforts and remain focused on a systematic approach, as this is a real head-scratcher of a problem. We definitely have indisputable proof of 12V at the starter solenoid. Jumping the switched relay terminals (30 and 87) engages the starter. I think, but can't recall, that we confirmed that the starter relay coil was seeing 12V. That leaves the starter relay coil's ground path as the problem.
 
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