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Con-Fused About 20A Fuse Popping like Popcorn

mphilleo

NAXJA Forum User
Location
Lincoln, ND
What a wild ride. After about a month, several hundred dollars and lot of black nitrile gloves, I've gotten my 1996 XJ baselined and up to snuff. I even made sure all the bulbs are correct to ensure correct amperage draw. But a problem I hope I might have somehow corrected is still raising its ugly head.

By process of elimination, it appears the 20A maxi fuse in the PDC under the hood blows every time I start the car. That is, I have no blinkers, hazards and brake light whenever I decide I want to operate the car. I have confirmed if the vehicle is off and I put in a new 20A fuse, I have working blinkers, hazards and brake light. Start the car? The fuse blows and those features are gone. All the fuses in the kick panel below the steering wheel are intact and the relay works fine when the fuse is intact to allow those features to work.

Has anyone else experienced this sort of problem? I'm not 100% certain whether the wiring harness for this '96 is for '96 and earlier years or '97 and up (as 1996 was a transitional year for the XJ), so I wouldn't even know what wiring diagram to refer to. Suffice it to say, this is pretty frustrating, so any help is greatly appreciated.
 
So let me read this back to you. You are saying if you simply turn on the key and have a new fuse, things work, but if you crank and start the engine, the fuse blows?

If you crank but don't allow it to start, does it blow the fuse as well?
 
Take a look at the wiring going from the back of the vehicle through the hatch. My 98 would pop a fuse every time I would turn the rear defrost on. Turns out the rear defrost is on the same circuit as the starter. Mine had wires broke and shorting to one another.
 
Well, sorry for the red herring. I spent a lot of time last night checking things. I could explain all the stuff I did but long story short and two test fuses later, I discovered application of the brake light is what's blowing the fuse. This is with accessories on and the vehicle off, so it has nothing to do with starting the Jeep.

Interestingly, it looks like the previous owner had put a splice on the white wire of the brake switch and had a blue wire coming off of that. Where it goes, I haven't determined yet, but it goes into the kick panel below the steering wheel. For giggles, I cleaned up the splice and taped it back up, put it back on and it blew another fuse. I have no idea what the purpose of this splice was as the Jeep, to my knowledge, has no immobilizer, ABS or remote starter.

At this point, I'm going to look for a short between the brake switch and the rear tail lights. I'll also check the grounds on the driver side rear quarter and any harness behind that panel.
 
Two problem spots I found.

Where the wires from the taillight assembly pass through the body. prime spot for rub throughs.

I had something similar once, I put one of the screws for the inner door sill cover through my harness during reassembly.
 
Typically the blue wire is for trailer brakes, it's wired from the dash to the rear access panel.
 
Two problem spots I found.

Where the wires from the taillight assembly pass through the body. prime spot for rub throughs.

I had something similar once, I put one of the screws for the inner door sill cover through my harness during reassembly.
Are you saying you looked behind the driverside cargo panel where the grounds are? Or is there anywhere else you suggest?


Typically the blue wire is for trailer brakes, it's wired from the dash to the rear access panel.
That would make sense. I'm not good with a DMM, but I tested at 200 ohms with one probe on the blue wire and one on ground and it showed 1 ., which I assume is infinite or nothing going through the wire. I assume that I can just disregard the wire then and tie it up out of the way?

I'm looking up ways to bench test the brake switch in the mean time, just to be sure. Is the trailer wiring harness that pile of wire that's usually sitting between the spare tire and the tailgate?

Last question. my Jeep didn't come with the optional 3rd brake light. I saw the plug loose behind the door panel so I wrapped the end with electrical tape and tied it away. That shouldn't be creating a short since it's a plastic fitting, right?
 
Have you pulled the brake light bulbs and tried again. When they burn out the filament can lead to a short in the bulb.
 
Are you saying you looked behind the driverside cargo panel where the grounds are? Or is there anywhere else you suggest?


That would make sense. I'm not good with a DMM, but I tested at 200 ohms with one probe on the blue wire and one on ground and it showed 1 ., which I assume is infinite or nothing going through the wire. I assume that I can just disregard the wire then and tie it up out of the way?

I'm looking up ways to bench test the brake switch in the mean time, just to be sure. Is the trailer wiring harness that pile of wire that's usually sitting between the spare tire and the tailgate?

Last question. my Jeep didn't come with the optional 3rd brake light. I saw the plug loose behind the door panel so I wrapped the end with electrical tape and tied it away. That shouldn't be creating a short since it's a plastic fitting, right?

Right behind the taillight assembly, take the taillight out (easy with a 96). There is some sheet metal behind the taillight assembly and the wires can get cut there.

You can remove the brake bulb like Old_man suggested at the same time. Inspect the wires as best you can and look for cuts.
 
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