My 87 XJ has been a solid runner, until this issue came up. It's a 4.0L 5 speed manual that has been in the family since it was new.
It recently developed an issue where the running/dash illumination fuse blows as soon as the switch is moved to that position.
I turned the lamp brightness all the CCW to isolate the dash lights from the running lights. No effect. The fuse still blows without hesitation.
I removed all the marking lights looking for a rubbed wire, none found.
The rig came with trailer wiring from the factory, so I disconnected the wire to the 5 way. Still a quick blow on the fuse.
I inspected the tailgate wiring at the feed through and the nylon sheath is still in place.
I can see the license plate/wiper/defroster plug on the chassis side behind the rear tailight assembly. Is there an access point for this behind the spare tire?
Is there somewhere where I can isolate the front marker lights from the rear marker lights to better localize the wiring issue?
Also, no side of rodent damage or nests anywhere on the rig. The barn cat must be doing a great job.

Guidance please...

John

 

Your major backend wiring hub is behind the spare tire. Your have to remove the tire and bracket. Also about 10 little screws from the plastic piece. The rear seat belt harness runs through the plastic, so you have to pull it put and lay it in your backseat. The grounds for your wiring are back there. They probably broke or are corroded. Any holes in the frame usually allow dirt and dust from the road to blow up into that compartment from your rear driver side tire.

 

This^^^.

 

Accessed the connectors behind the Driver's side rear panel and disconnected all of them.
Installed a new fuse and pulled the light switch **** to turn on the running lights.
Pop, another instant fuse blow. My thought is to pull the instrument panel and remove that from the possibilities before going under the hood.
Seem reasonable? Other suggestions?

 

Install a new radio lately?

 

The same radio had been in place for almost 10 years.
I was planning on looking in the dash area, just because it's more accessible.

 

Look around the headlight switch to see if it's melted.

 

I'll take a look at the switch and I even have a spare.

 

Most likely it's what the others are saying but if the wiring looks sound, remove light bulbs and see if it still blows with no load to drive. That would indicate a short to ground in the harness.

I had an issue with mine where the wrong bulb was in one of the running lights and it was all rusted up. I removed it without checking it, cleaned it up and pushed it back in. It blew the fuse instantly. Then I found it was the wrong bulb. Running lights are 2057 while turn signals are 1156. One has two connections on the bottom and the other has only one (which will short the circuit if pushed in).

 

What fuse is popping and where?

Make sure you identify the related circuits and inspect all the connectors on that circuit

 

It's the 10A parking light fuse.
Been working on other projects of late and haven't had any time to work on it.
I'm going to look at the dashboard wiring again, as I recalled one lamp that comes on with the lights.