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strange electrical issue

tjmotter

NAXJA Forum User
NAXJA Member
Location
Texas
'90 XJ 4.0 Automatic.

The strangest thing just happened to me and I am wondering if anyone else has seen this or can offer some insights on what might be happening.

The XJ is working great but while stopped waiting for food pickup, I decided to turn on the headlights and suddenly my temp gauge pegged. Turned the lights off and the gauge dropped back to normal. Tried this a couple of times with the same result.

After picking up dinner (vehicle running all the time), I started to drive home and decided to try it again. This time the headlights came on and while the gauge slowly moved up a couple of degrees, it didn't peg. Left the lights on for the rest of the drive home and saw no other issues.

One thing that may be related is that the temp gauge has always pegged when the starter is running but as soon as the engine starts, it drops to normal.

I recently went through this Jeep from front to back checking every connection, updating all the grounds and fixing a couple of nit items like slow power windows. I had upgraded the power/neg cables a couple of years ago (custom made kit by Neal) and also added the headlight mod that powers the headlights directly from the battery through a set of relays that are triggered by the headlight switch. Starter and alternator have less than 500 miles on them.

Looking at the schematics, I don't see anything that even remotely connects the temp gauge to the headlights so the only thing I can think to check is the connections on the back of the gauge cluster. I had the cluster out a couple of months ago and they looked fresh but I am out of ideas.

Anyone seen this before?
 
Last edited:
Re: strange electrical issue - fixed

Upon further testing I found that with the ignition off and the headlights on, the gauge would climb up until it pegged. Once I turned the ignition on it would drop back down to normal so I suspected a ground issue on the instrument cluster.

Pulled the instrument cluster out and found that I was seeing a high resistance between the ground post of the temp gauge and the copper strip. Removed the screw, cleaned the contacts and the gauge is working perfectly again.

Updated in the event that anyone else finds this issue.
 
Thanks. Already done. In fact, I not only have a wire going from the stud to the screw under the dash, I also have a continuous wire connection from this point all the way back to the battery. When I received my ground upgrade wires, there was one that was long enough to travel from the engine stud (just back from the dipstick) all the way to the mount point on the firewall. Since my battery is connected to the same point, I have a continuous ground line running all the way to the firewall so just to finish the job, I strung a wire from that point through the speedo wire hole and connected it to the wire I put on the stud, soldered them together and added an eyelet and then connected this to the existing ground wire going to the underside of the dash. It might seem like overkill but everything seems to be working better and I am pretty certain that this '90 XJ has one of the best ground circuit in the world right now.:yap:
 
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