Electrical gremlins

So fresh of off fixing my leaking exhaust manifold, it's on to the next issue thats been plaguing the Jeep...

gauge cluster (only the tach and speedo it seems) is sensitive to power draws.
they seem OK until another accessory is turned on, then they go erratic, or stop working completely.. the more I turn on the the worse it gets..

So far I've checked and cleaned all the major grounds, checked the PCM connections, and cleaned/checked all the sensors on the throttle body.

thinking maybe the cluster itself, PCM, or another ground I missed somewhere.. :dunno:


Here's a video of the issue for reference, ac is on the whole time with various accessory's turned on and off...
http://youtu.be/dJqfX1aNJHI

1996 XJ, 4.0/5sp

Also forgot to mention, the volt gauge does work at all, but the battery/alt check out OK..

Ok, so maybe someone can answer this.. shouldn't the voltage at the contact screws on the back of the gauge cluster be 12v?

I tested with a good ground and was getting ~8v at the screws..I know they get power from the PCM, so maybe that's correct.. :dunno:

Sounds like a ground issue. Grounds get corroded, wire breaks or whatever and the electricity tries to find a way to ground, sometimes backwards down another circuit. And/or the ground has so much resistance the electricity backs up in the ground circuit, especially when multiple accessories are used at the same time. Both ways may cause serious problems.

I'm thinking you may have a bus issue, a partial short someplace in a circuit that supplies power to the gauges or *a ground issue*.

The G 106 (double) ground ring next to the PCM is one place to check. Mine had almost 2 ohms of resistance when I checked it. I cut the ground rings off, crimped and soldered some new ones on, sanded the metal and put a new screw and star ring washers in there.

The G 108 is another, I haven't found the G 108 ground ring yet. Best guess is it is behind the drivers side kick panel or maybe the dash metal cross brace near the drivers side kick panel.

I've been thinking about soldering in some extra ground splices in both circuits and maybe another at the ground wire for the window washer motors. Jumping the ground at the windshield washer motors to a place on the passengers side wheel well would give that circuit a chance to ground without going through a dozen splices.

I'm having what I believe are ground issues in the same circuit (maybe) you seem to be having trouble with. Some of the same issues like erratic volt meter function and some others like random door buzzer, constant seat belt warning light and erratic windshield washer function. I'm suspecting I have ground issue. None of this stuff was acting up until a mechanic swapped out my tranny and replaced the drivers side window motor.

Hard to tell how grounds are going to interact when one messes up. I also found high resistance in the head to firewall ground strap, corrosion between the strap end and the firewall. About half my ground issues disappeared after I cleaned that up. A few other problems disappeared after I fixed the G 106 ground. Next on my list is the G 108 ground and my tranny ground (just a hunch).

Yeah cleaning the major grounds didn't make any difference, so I'm in the process of hunting all the smaller ones down. Haven't been able to find the G106 though, is it possibly a renix ground location?

1996XJ40 said:

Yeah cleaning the major grounds didn't make any difference, so I'm in the process of hunting all the smaller ones down. Haven't been able to find the G106 though, is it possibly a renix ground location?

Click to expand...

On my 96 it is maybe four inches (just a guess) from the PCM towards the firewall. Two black wires (rings) screwed into the inner fender well. It doesn't look like much, but a bunch of accessories and other stuff ends up grounded there after passing through a bunch of splices.

I haven't found the G 108 myself yet, though I haven't really looked hard, higher priority stuff I have to fix first. Some of my instruments are quirky and were fine before a mechanic changed out my drivers side window motor. The main reason I hate giving my Jeep up to a shop, invariably I spend more time trying to fix their fark ups than it would have taken me to do the job myself.

I don't have a 96 FSM, this is for a 97, the same ground is called G 104/G 105 in the 95 FSM.


bilder kostenlos hochladen

Well I found the G106 ground (thanks 8Mud) and cleaned it up, as well as replaced the 3 main battery ground wires, since they were starting to corrode internally anyways.

The Volt gauge still reads a little low, but it works now, and no more erratic tach/speedo!

However... now I'm getting a P0123 code and my idle is rough... took the TPS off and it makes crunching noises when actuated...it never ends...

Just to update this thread one more time in case it helps anyone else with this issue...

I was still having gauge issues, and found what was likely the original cause..
The #17 fuse (7.5a) was corroded, and the copper contacts that hold the fuse were cracked/broken.. bypassed the fuse panel with an inline fuse holder and all is good.. :cheers: