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

[macleanflood]

I really feel like it was supposed to be there. I may go put it back on after my meeting ends, to see if it makes a difference now that the ground point is cleaned up.

Not saying what's right or wrong just adding my visual observations.

Either way that wire is probably inconsequential to your issue and you need to deloom the harness from G105/107 to the terminal and inspect. My guess is one of the factory crimps is corroded.

-Mac

 

[Gormy]

I don't use that type of battery terminal (that clamp the bare end of the cable) anymore. Over the years, I've had all kinds of trouble with them being able to transfer high current loads. I'm not saying that's your problem, but I'd crimp a ring terminal on the cable and use a screw terminal connection at the battery.

Just for grins, try connecting a jumper cable from battery negative to anywhere on the engine and give the key a turn. That will ensure that that cable is not your problem. Then, as you said, you'll have to start digging into the three sections of harness I mentioned earlier.

I bought these terminals just to use for testing everything while I am taking the cables on and off and trying to diagnose these issues. And if there are any draws, it won't kill the battery if I don't go through all the work to loosen the "normal" terminal clamps and take them off each time. I'll swap these out for better ones once all the electrical issues are resolved.

I will try the jumper method after my meeting.

 

[mrblaine]

Yeah, but static discharge is much misunderstood. I wouldn't be surprised if it was added, and then discovered that it did nothing, so it was removed. I've seen that type of thing happen many times (not a static ground strap, but things done that don't work that quietly disappear.)

While I am not much of a fan, Mythbusters did an episode trying to blow up anything with all the warnings that are posted on gas pumps that will kill you. IIRC, it was near impossible even under their most contrived circumstances to get a spark and fumes to do much. That and you only need a small bit of smarts to figure out most of it is CYA with zero basis in reality. If you really had to shut your car off to put fuel in it, there would be one gas pump on an isolated island with fume fans that allowed one vehicle at a time to use the pump. Not sure how they overlook that no matter what you are doing, another vehicle pulls up within a few feet with a running engine while you are fueling.

Automotive engineers are always learning how their old ideas were stupid. Trust me, I speak from experience.

It isn't just engineers. We all learn from our mistakes, that's how we get better.

 

[Gormy]

I don't use that type of battery terminal (that clamp the bare end of the cable) anymore. Over the years, I've had all kinds of trouble with them being able to transfer high current loads. I'm not saying that's your problem, but I'd crimp a ring terminal on the cable and use a screw terminal connection at the battery.

Just for grins, try connecting a jumper cable from battery negative to anywhere on the engine and give the key a turn. That will ensure that that cable is not your problem. Then, as you said, you'll have to start digging into the three sections of harness I mentioned earlier.

I just ran a jumper from the G105/107 ground bolt to the negative terminal and I have no crank, no start, and a NO BUS issue still. So now I start tracking the BK/TN wire from the ground point to the PCM?

 

[mrblaine]

I just ran a jumper from the G105/107 ground bolt to the negative terminal and I have no crank, no start, and a NO BUS issue still. So now I start tracking the BK/TN wire from the ground point to the PCM?

There is a reasonably well known issue with a ground splice in the harness behind the head or roughly in that area. It is a splice where they bring several ground wires together, solder them, cover the joint with heat shrink and then the single goes over to the PCM area. The joint corrodes and you wind up with lost or intermittent grounding.

 

[sab]

I just ran a jumper from the G105/107 ground bolt to the negative terminal and I have no crank, no start, and a NO BUS issue still. So now I start tracking the BK/TN wire from the ground point to the PCM?

Yes

 

[Gormy]

Yes

I haven’t taken the loom off of all of it yet, but I did take it off at the junctions. Everything looks good near the ground bolt. The ground splice and Blaine mentioned doesn’t look bad unless it’s broken inside. And at the plug at the PCM it looks good too. Do I need to tear apart the splice?

 

[sab]

While I am not much of a fan, Mythbusters did an episode trying to blow up anything with all the warnings that are posted on gas pumps that will kill you. IIRC, it was near impossible even under their most contrived circumstances to get a spark and fumes to do much. That and you only need a small bit of smarts to figure out most of it is CYA with zero basis in reality. If you really had to shut your car off to put fuel in it, there would be one gas pump on an isolated island with fume fans that allowed one vehicle at a time to use the pump. Not sure how they overlook that no matter what you are doing, another vehicle pulls up within a few feet with a running engine while you are fueling.

Yes, the fact that in all my years, I can't once remember a massive fire at a gas station supports that.

 

[sab]

The ground splice and Blaine mentioned doesn’t look bad unless it’s broken inside.

Is it orange inside the clear heat shrink from corrosion? Remember, that 0.77 ohm resistance is enough to drop the voltage at the relay coil and render it unable to switch the relay. All it takes is a little corrosion on the surfaces of the wire and splice to create a small bit of resistance.

 

[Gormy]

Is it orange inside the clear heat shrink from corrosion? Remember, that 0.77 ohm resistance is enough to drop the voltage at the relay coil and render it unable to switch the relay. All it takes is a little corrosion on the surfaces of the wire and splice to create a small bit of resistance.

It could be. But is there a simpler explanation that I am overlooking? This wiring harness started the Jeep last November just fine without any NO BUS issues. It sat until two weeks ago when I tried firing it up again. Is it likely that the inside of this splice corroded during that time it sat in my garage and that's what is causing it? Or is it that I likely still have a ground issue elsewhere?

 

[sab]

But is there a simpler explanation that I am overlooking?

Using visibility as a way to judge the quality of a ground is useless - you can't usually see ground problems where just a little resistance is created. You can't see voltage, current, or resistance, remember. The 0.77 ohms you tested tells me that it's an issue. The way ground problems work is that the resulting resistance can vary with load. The load a multimeter puts on the connection is extremely low compared to the relay coil (after all, if the load was high, the multimeter itself would affect the readings so much as to be inaccurate.) With more current, the resistance could be higher. That's why people often times use test lights instead of multimeters to find ground problems.

This wiring harness started the Jeep last November just fine without any NO BUS issues. It sat until two weeks ago when I tried firing it up again.

That wiring harness may have started a Jeep in November, but with the work you've done, it's not at all the same Jeep. It's entirely possible that your relay coil was finding a ground through some other path that is no longer there.

the Jeep ... sat until two weeks ago when I tried firing it up again. Is it likely that the inside of this splice corroded during that time it sat in my garage and that's what is causing it?

Not likely, unless you had it open to the elements for seven months.

Or is it that I likely still have a ground issue elsewhere?

It's possible, for sure. Not sure about likely. As this journey has unfolded, it's proven one thing. Electrical diagnosis is frustrating, but perseverance and diligence are vital.

 

[Gormy]

You'll find locations of the connectors, splices, and grounds in the Factory Service Manual (FSM). Use that to figure out where they are. I would start with Ground G105. If it's a ring eye screwed to the body, remove it, clean it and the body contact point up with sandpaper, and reinstall it. Then check continuity from battery negative back to the BR/LB terminal on the starter relay. If you have less than 0.1 ohms, that ground point was the problem. If not, you have to dig into the harness.

I just tried doing this again. Took it off the firewall, sanded the ring eye connector and the bolt, sanded some paint off the firewall to give it more grounding area. Rechecked the continuity and it's 0.76 ohms. I think it must be in the wire harness somewhere. The grounds under the hood have all been taken apart again and recleaned/sanded today, and still no change...

 

[Mike_H]

Before I tear apart the harness, I think I would start installing jumpers to see if we are indeed on the right path. If you can install jumpers along the circuit path, to know that it will work how it’s supposed to, that will help us isolate what is going on. If you still have the same problem with a known good circuit, then you have something else going on.

 

[Gormy]

Before I tear apart the harness, I think I would start installing jumpers to see if we are indeed on the right path. If you can install jumpers along the circuit path, to know that it will work how it’s supposed to, that will help us isolate what is going on. If you still have the same problem with a known good circuit, then you have something else going on.

I was thinking about this and it was going to be my next question. Can I splice a wire into the BL/TN wire at the engine ground and run it to the harness end at the PCM, and if that fires it up (it'll bypass the coil so likely won't fix the NO BUS issue) then it's likely in this harness somewhere? Or am I just not thinking this through correctly with my limited understanding of this?

 

[Mike_H]

Trace the signal in your mind and follow the schematic. Start at one end or the other and use jumpers to connect the actual components. When you get it to start, you’ve isolated the section of harness that is the problem.

You could also do it with a meter, looking for the jump in resistance.

 

[Gormy]

Using continuity. There are three sections of harness to test:

View attachment 535801

You'll find locations of the connectors, splices, and grounds in the Factory Service Manual (FSM). Use that to figure out where they are. I would start with Ground G105. If it's a ring eye screwed to the body, remove it, clean it and the body contact point up with sandpaper, and reinstall it. Then check continuity from battery negative back to the BR/LB terminal on the starter relay. If you have less than 0.1 ohms, that ground point was the problem. If not, you have to dig into the harness.

Check continuity on each of the three sections above. The little numbers next to the double-chevrons are the cavity locations in the connectors. Look up the connector pin-out chart in the FSM to figure out which one it is (you can also go by wire colors, which are also in the connector charts). For each of the three sections, or any combination thereof, you should get less than 0.1 ohms, meaning you have continuity. If you can pin it down to one (or more - maybe there are multiple problems) section of harness having resistance that's too high, then you have to look at each end, where the terminals are crimped, and within the harness, for damage. Find it, repair it, and you'll be golden.

Good Luck!

Sab, forgive me because I may really frustrate you here.

I opened up the FSM and worked to track down all these connectors. I found C154 is by the transmission. I went to that one and found a broken black wire. I hoped that was the cause of all my issues. It was not. I cleaned it up and put a connector on it. Picture of broken wire below.


I tested it on my multimeter, and had to move the dial to the 200 ohm setting. The result was 0.4.

I cannot find what is meant by the C154 Manual Transmission Jumper. It seems it goes in as a black wire and comes out brown/light blue? I can't figure out how to test #2 in your diagram.

For #3, I tested it from the S134 connecter at the firewall to the starter relay. The reading again was 0.3 on the 200 ohm setting. Picture below.


Where do I go from here?

 

[Gormy]

Using continuity. There are three sections of harness to test:

View attachment 535801

You'll find locations of the connectors, splices, and grounds in the Factory Service Manual (FSM). Use that to figure out where they are. I would start with Ground G105. If it's a ring eye screwed to the body, remove it, clean it and the body contact point up with sandpaper, and reinstall it. Then check continuity from battery negative back to the BR/LB terminal on the starter relay. If you have less than 0.1 ohms, that ground point was the problem. If not, you have to dig into the harness.

Check continuity on each of the three sections above. The little numbers next to the double-chevrons are the cavity locations in the connectors. Look up the connector pin-out chart in the FSM to figure out which one it is (you can also go by wire colors, which are also in the connector charts). For each of the three sections, or any combination thereof, you should get less than 0.1 ohms, meaning you have continuity. If you can pin it down to one (or more - maybe there are multiple problems) section of harness having resistance that's too high, then you have to look at each end, where the terminals are crimped, and within the harness, for damage. Find it, repair it, and you'll be golden.

Good Luck!

Sab, forgive me because I may really frustrate you here.

I opened up the FSM and worked to track down all these connectors. I found C154 is by the transmission. I went to that one and found a broken black wire. I hoped that was the cause of all my issues. It was not. I cleaned it up and put a connector on it. Picture of broken wire below.


I tested from G105 to C154 on my multimeter, and had to move the dial to the 200 ohm setting. The result was 0.4.

I cannot find what is meant by the C154 Manual Transmission Jumper. It seems it goes in as a black wire and comes out brown/light blue? I can't figure out how to test #2 in your diagram.

For #3, I tested it from the S134 connecter at the firewall to the starter relay. The reading again was 0.3 on the 200 ohm setting. Picture below.


Where do I go from here?

 

[Gormy]

Well.... we're going backwards now. I fixed the broken wire by the trans, in what I believe is C154. I removed the ground cable that grounded G105 to the frame. Everything else should still be attached as it was previously, just de-loomed the wire harnesses. I couldn't start it up that way, so I reverted back to trying to ground the BR/LB wire of the relay to the negative post of the battery. That will not start the Jeep now. The only way to start it is to jump the starter from the battery...

 

[sab]

Sab, forgive me because I may really frustrate you here.

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 opened up the FSM and worked to track down all these connectors. I found C154 is by the transmission. I went to that one and found a broken black wire. I hoped that was the cause of all my issues. It was not. I cleaned it up and put a connector on it. Picture of broken wire below.

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:

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!

I tested from G105 to C154 on my multimeter, and had to move the dial to the 200 ohm setting. The result was 0.4.

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

I cannot find what is meant by the C154 Manual Transmission Jumper. It seems it goes in as a black wire and comes out brown/light blue? I can't figure out how to test #2 in your diagram.

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?

For #3, I tested it from the S134 connecter at the firewall to the starter relay. The reading again was 0.3 on the 200 ohm setting. Picture below.

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:

Where do I go from here?

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.

 

[sab]

Well.... we're going backwards now.

Really? I feel like we have plenty of forward momentum. Look how much we've learned from this thread. Stay positive!

I fixed the broken wire by the trans, in what I believe is C154. I removed the ground cable that grounded G105 to the frame. Everything else should still be attached as it was previously, just de-loomed the wire harnesses. I couldn't start it up that way, so I reverted back to trying to ground the BR/LB wire of the relay to the negative post of the battery. That will not start the Jeep now. The only way to start it is to jump the starter from the battery...

I was writing my response to your previous post when this came in and sometimes if I look at new posts, I lose my work in progress (the previous post took nearly an hour to research and send). I didn't read it until I posted that last post.

If your jumper from BR/LB on the relay socket to Batt Neg no longer works, the most likely cause is that your "repair" actually connected two wires that weren't meant to be connected (you can always cut it and try your ground jumper again to confirm). I can't tell from your photo whether that's a possibility or not. However, as I said in my previous post:

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.

Note my edit - "of" was supposed to be "or"

I can't tell what color the wires are in that photo of the broken wire, and they look to be very dirty. Can you confirm what wire colors run from there to the connector? And, like I said earlier, confirm that there is a jumper from Pin 1 to Pin 3...