YJ wiring nightmare

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Vincent Gendron

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Joined
Apr 13, 2024
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3
Location
Murfreesboro TN
Hello everyone, we are working on my sister's YJ and here is everything going wrong...

Initial issue was she kept blowing fuses for hazards and stop lights. Second issue was her instrument panel didn't light up when turning headlights on. Then the harness running up to the brake light switch was getting scorching hot when testing things. Now we can't get her radio to turn on, the cigarette lighter wire we used for the AC is not getting power, dash and instruments still don't light up, and we broke the brake light switch. We have the dash mostly off, and from what we can tell there are no bare wires, no bad grounds, but we can't figure out what to even do next. Could her fuse box be bad from blowing too many fuses? Is her wiring harness bad? Is it the battery? Alternator?
She also said her headlights dim when applying the brakes. It's an absolute nightmare.
 
Sounds to me bad ground(s). Hot wires, dimming lights and notoriously bad grounds on jeeps. Dirty headlight plugs, grounds there. The dash cluster is also grounded. You can also add grounds anywhere, never hurts. Just make sure you go to clean metal where they are landed.
 
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As Gila mentioned. Start with your grounds, especially battery to engine and chassis grounds, your battery cables can look good on the outside but will be a tube of solid corrosion on the inside, if you don't know the last time the cables were replaced go ahead and do it. THere are good kits out there or you can take the old ones to the parts store and build some from what they have there, the last set of battery cables I did at the parts store ran me 60 dollars for the cables and hardware and myself at the counter guy built them with their tools on the counter before I left.

Bad grounds=high resistance=lots of heat build up. They can also cause lots of weird electrical gremlins on these Jeeps as lots the sensors depend on a 5V reference signal.
 
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So we found a relay that was not being powered. Connected power to the 30 on the relay and the instrument cluster lights up again. We got a new brake light switch and installed it. However, now the issue is when applying brakes, the fuse pops. Do you all have any recommendations on how to find where that is shorting out?
 
Chase the wires. The taillight wiring runs under the interior edge of the tub on the driver's side then though a grommet in the back driver's corner of the tub to the driver's side tail light then across the rear crossmember to the other light. Start inspecting from there and see what you find. If I had to guess it's probably in the wiring past the grommet by one of the tail lights.
 
We followed the wires all the way and found nothing wrong with them. What is strange is they work fine normally when applying brakes. Tested the blinkers and they worked fine. Then when turning the headlights on, the blinkers are slower. Then applying brakes, the left light shorts out and the right one continues to work. Then when you turn the headlights back off the left still doesn't work. It is not until you turn the vehicle off and on again that the left one starts working.
 
Are these standard bulbs or LED? Have you checked out the flasher relay?

What about the grounds as suggested above have you messed with those or replaced them at all? This really sounds like some kind of weird ground issue.
 
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