Working through final wiring issues on my build and I'm stumped
- Thread starter Gormy
- Start date
Suggestion...do you have a neighbor with another multimeter you could compare results with? With another meter we could quickly see if there's any discrepancy between the two...there will be some...
I just got out of my meetings. I'm going to go run and buy a new one.
I just got out of my meetings. I'm going to go run and buy a new one.
Update: New multimeter purchased.
Results:
- G105 to the BR/LB wire on the back of the PDC: 0.00 ohms
- G105 to battery negative post (as requested earlier): 0.00 ohms
- Battery negative post to BR/LB wire on the back of the PDC: 0.00 ohms. (audible beep to confirm a circuit) - Edited to add
I confirmed there is a circuit being tested by using the audible beep setting. So the 0.00 ohms is accurate, I believe.
I tested the circuit with the C154 harness unplugged. It read 751 ohms.
If I am understanding everything correctly so far (that could be wishful thinking at this point), this is a perfect circuit now with the black ground wire reattached at the transmission jumper. There is no resistance from what I am seeing.
With all of that fixed (if it's fixed), we've made progress, but the Jeep still will not start and I have a NO BUS issue still.
Side note: I don't believe it is the issue, but I now have both new parts of the ignition here. I can swap that out to see if it'll fix it. But since I could previously start it by grounding the BR/LB wire in the PDC to ground, I know the ignition was at least working correctly two days ago, so I am hesitant to introduce any new changes into this until it is narrowed down.
Results:
- G105 to the BR/LB wire on the back of the PDC: 0.00 ohms
- G105 to battery negative post (as requested earlier): 0.00 ohms
- Battery negative post to BR/LB wire on the back of the PDC: 0.00 ohms. (audible beep to confirm a circuit) - Edited to add
I confirmed there is a circuit being tested by using the audible beep setting. So the 0.00 ohms is accurate, I believe.
I tested the circuit with the C154 harness unplugged. It read 751 ohms.
If I am understanding everything correctly so far (that could be wishful thinking at this point), this is a perfect circuit now with the black ground wire reattached at the transmission jumper. There is no resistance from what I am seeing.
With all of that fixed (if it's fixed), we've made progress, but the Jeep still will not start and I have a NO BUS issue still.
Side note: I don't believe it is the issue, but I now have both new parts of the ignition here. I can swap that out to see if it'll fix it. But since I could previously start it by grounding the BR/LB wire in the PDC to ground, I know the ignition was at least working correctly two days ago, so I am hesitant to introduce any new changes into this until it is narrowed down.
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So, we have two meters that read differently...We don't know if the new one is correct or if the old one is correct.
BIG UPDATE!!
There appears to be no less than THREE separate issues on this Jeep that are causing what I am chasing down.
For the heck of it, I popped the ignition switch out and tried starting it with a screwdriver. It fired right up! It did not do that before we found the ground issue at the transmission jumper.
With all of the broken ground issue figured out (issue #1), it will now fire up. I will replace the ignition switch and actuator now (not sure why the relay behind the glovebox is clicking when I try starting the Jeep if the actuator isn't turning the ignition switch). As long as the ignition and actuator work, all I am left with is the NO BUS issue (issue 3). I have cleaned all the terminals I can find, including the ones behind the instrument cluster, and it won't resolve the issue.
There appears to be no less than THREE separate issues on this Jeep that are causing what I am chasing down.
For the heck of it, I popped the ignition switch out and tried starting it with a screwdriver. It fired right up! It did not do that before we found the ground issue at the transmission jumper.
With all of the broken ground issue figured out (issue #1), it will now fire up. I will replace the ignition switch and actuator now (not sure why the relay behind the glovebox is clicking when I try starting the Jeep if the actuator isn't turning the ignition switch). As long as the ignition and actuator work, all I am left with is the NO BUS issue (issue 3). I have cleaned all the terminals I can find, including the ones behind the instrument cluster, and it won't resolve the issue.
Or I guess I won’t be replacing the switch. The one I waited a long time for isn’t even close to being correct.
Good! Klein makes decent stuff. Not top of the line (Fluke is that, but you pay for it), but certainly capable of most work.
That audible beep function is commonly called the continuity setting. Looks like all this time your meter was leading us astray! Man-o-man..,
By "the circuit," do you mean you put one probe on C154 Pin 1 and the other on C154 Pin 3 with C154 unplugged. If so, I guess it's time to switch back to the didactic method. Nobody has responded, and there's a very important lesson there. By the way (again assuming I'm interpreting "the circuit" correctly) - stop checking that! You'll see why shortly.
I'm still scratching my head here. Some very odd behavior. Some of your symptoms match what happens when the ignition switch is bad (they usually fail intermittently, from what I've seen on the forum, and how mine failed.) Other symptoms still look like a bad ground or other connection.
Ok, it's time to discuss this post. Not a soul has responded, and of everything in this thread, I think this is the most advanced concept to understand, but it's also a very important concept. So, let me put this Socratic ball cap down, and put my didactic cowboy hat (my preferred head wear) back on...
A multimeter, when measuring resistance, applies a small voltage across the leads, the meter measures the resulting current and uses ohms law (Voltage = Current x Resistance, or V=IR) to determine the resistance, and that resistance is displayed on the meter's display. If there is no connection between the two points being measured, it's an open circuit with infinite resistance - current will not flow. In that case, the display will read something indicating open circuit (meters vary on what they display).
So, knowing that, is there a complete circuit to be measured with the probes at Pins 1 and 3 on C154? At first glance, I think most people's instinct is to say, "no, there is not - it's an open circuit. If you start at Pin 1 and follow the wires, you can't end up at Pin 3." There's no loop, right?
Well, no, not right. Yes, you do need a loop. However, there are actually many loops there, you just can't see them. Every one of those dashed boxes is a component - this schematic is incomplete. It doesn't show the other connections to those dashed boxes. Even G105 has more going on (it's not the dead end it looks to be), and that's key to understanding what you're measuring in the schematic above.
If you've been following along, you may recall that G107 is another ring eye on the same bolt to which G105's ring eye is attached. The other end of G107's cable is at the negative post on the battery. So, if you continue from G105, now off the schematic, you go directly to G107 and then from G107 to the negative post on the battery through that larger gauge main engine ground cable. Then, you continue through the battery from the negative post to the cathode plates, through the acid to the anode plates, and finally to the positive post. Still not a circuit though, right? How do we get from the battery's positive post to Pin 3 to complete the circuit we're measuring?
Through all of those dashed components, of course! Every one of them needs a complete circuit to operate, after all. Since we're doing our tests mainly with the ignition off, some of those components are open-circuit and not contributing. Others, however, are very complicated devices (like the PCM), or have their own "black boxes" on the positive sides of the dashed boxes above (like the oxygen sensors), and I have no idea what's inside those devices.
It's all these circuits that combine to make one very big, very complicated circuit, and I wouldn't even attempt to guess what resistance value to detect when testing as shown above. In fact, I would venture to guess that nobody in the world could tell you that without hours and hours of research. And that is why testing resistance as shown above doesn't really help us. Who knows what the value should be?
Thank you everyone that spent the time walking me through this. And especially to Sab for going above and beyond with a phone call, text messages, and the patience to show me how to better understand the wiring diagrams in the FSM.
I don't like reading through these long threads to not find the solution at the end, so I am back to update everyone with what the findings were.
There were three main issues I was chasing
- The broken ground wire at the C154 harness down by the transmission. This was the biggest issue, and it likely occurred when I took the drivetrain out of the old frame, had it sitting in the garage while I did all the clutch, flywheel, pressure plate, etc., and then reinstalled it in the new frame. Most of the issue ties back to this broken ground wire, and as I expected, it was human error. I now know better to look over harnesses when they are out of the vehicle.
- The ignition switch is starting to go bad. When Sab had me ground the starter relay to the negative post of the battery, I was able to turn the Jeep on with the ignition. Sometime between that point in time and the next time I tried starting it with the ground wire fixed, without touching anything in the ignition, the switch was malfunctioning. Removing it and turning it with a screwdriver allowed it to start right up. I then reinstalled it and it is working again (new switch is here and I will replace it if it continues to act up). This unknown issue made it more difficult to track down as it started perfectly once and then not at all the next 40+ times.
- My old multimeter was not accurate and has since found a new home in the trash barrel. The new one gave better readings.
The other issue I have been chasing is the NO BUS issue. Last weekend after getting it fired up and driving, after being on the road for 2-3 minutes, all the gauges began to work. Then the next time I drove they didn't. Then they did. Then they didn't... Sab helped me figure out where the wires are that run from the PCM to the gauges, and they both have continuity. So it's likely going to be an issue in the PCM or the instrument cluster itself. I need to plug a code reader in one of the times that the gauges are working to see why I have a check engine light on. The airbag light is also on. And the NO BUS, check engine light (data link connector) and the airbag light are all tied into the same two twisted wires that run from the PCM to the gauge cluster. I will continue to look into that as time goes on, but I'm not as worried at the moment. I have a Jeep that starts up and drives.
This week the Jeep is at the shop getting an alignment, having all the new suspension and steering checked over, and trying to figure out what is causing a clunk and binding noises. That's likely all tied to everything in the suspension and steering being brand new and never adjusted perfectly. With any luck I'll have it back today or tomorrow and be driving it this weekend.
Thank you all again! There's a great community in this forum!
I don't like reading through these long threads to not find the solution at the end, so I am back to update everyone with what the findings were.
There were three main issues I was chasing
- The broken ground wire at the C154 harness down by the transmission. This was the biggest issue, and it likely occurred when I took the drivetrain out of the old frame, had it sitting in the garage while I did all the clutch, flywheel, pressure plate, etc., and then reinstalled it in the new frame. Most of the issue ties back to this broken ground wire, and as I expected, it was human error. I now know better to look over harnesses when they are out of the vehicle.
- The ignition switch is starting to go bad. When Sab had me ground the starter relay to the negative post of the battery, I was able to turn the Jeep on with the ignition. Sometime between that point in time and the next time I tried starting it with the ground wire fixed, without touching anything in the ignition, the switch was malfunctioning. Removing it and turning it with a screwdriver allowed it to start right up. I then reinstalled it and it is working again (new switch is here and I will replace it if it continues to act up). This unknown issue made it more difficult to track down as it started perfectly once and then not at all the next 40+ times.
- My old multimeter was not accurate and has since found a new home in the trash barrel. The new one gave better readings.
The other issue I have been chasing is the NO BUS issue. Last weekend after getting it fired up and driving, after being on the road for 2-3 minutes, all the gauges began to work. Then the next time I drove they didn't. Then they did. Then they didn't... Sab helped me figure out where the wires are that run from the PCM to the gauges, and they both have continuity. So it's likely going to be an issue in the PCM or the instrument cluster itself. I need to plug a code reader in one of the times that the gauges are working to see why I have a check engine light on. The airbag light is also on. And the NO BUS, check engine light (data link connector) and the airbag light are all tied into the same two twisted wires that run from the PCM to the gauge cluster. I will continue to look into that as time goes on, but I'm not as worried at the moment. I have a Jeep that starts up and drives.
This week the Jeep is at the shop getting an alignment, having all the new suspension and steering checked over, and trying to figure out what is causing a clunk and binding noises. That's likely all tied to everything in the suspension and steering being brand new and never adjusted perfectly. With any luck I'll have it back today or tomorrow and be driving it this weekend.
Thank you all again! There's a great community in this forum!