help me diagnose this wiring gremlin

brought my truck to get inspected, shop fails b/c no rear running lights.
I get home, pop out the (blown) fuse, pop a new one in, same size, everything works great. OK, just an every day, normal xj thing. Shop said they tried replacing fuses, I figure they were just blowing me off..

Anyway, I decide to check everything out anyway, since I wanted to run a license plate camera, so I pulled everything from rear to dash on the driver's side --- rear hatch trim, all the drivers front/rear trim. I traced all the wires... no rot, no grounding that I can tell. All the lights look good.

put everything back together, start the truck up and ... POP. fuse blown. Dash board lights out, rear running lights out. Front head lights work, brakes work, rev lights work, and signals all work.

this is after almost a full day of work, with everything ripped out.... owners manual says 15amp fuse (the "hzd stop" fuse is the one blowing). I drop in a 20amp fuse. works fine with truck off, start it, pop.
Drop in a 30amp fuse, now it works fine, ran it for 30 minutes with no pop.


Any idea whats going on? A surge or something somewhere?
I'll say that I've been running with this setup for over a year, haven't really messed around with the electrical in a while (I did flip the truck last year, but none of the panels I had to repalce were near anything electrical)

any help appreciated.

Failure of the tailgate wire harness is almost as common as failure of the drivers door wire harness. Visually inspect the wires at/near the flexible rubber boots. and continuity test the tailgate wire harness. Inspect any trailer wiring, and consider temporarily removing it. Inspect the wire plugs, relays, and grounding points behind the spare tire and plastic trim panel. Inspect the taillight socket wires for evidence of pinched wires or other careless damage.

As Tim says -- you gotta look at the wires in the boot at at the top of the rear hatch -- your short is probably there

Not a good idea to go to a 30 amp fuse -- a direct short in small wire could melt down with a fuse that large and cause a whole lot more problems

First off, I'd replace the fuse with the stock rating till you locate the issue. it's much easier to repair a short when the harness isn't melted.

The easiest way to find the short is next time the fuse pops, replace the fuse with a light bulb, light a headlight. When the circuit has power and is shorted the headlight should light up pretty bright. Then go and start messing with the harness in your jeep, if the light goes dim or out, the last thing you touched or moved most likely has your short in it.

Thanks... agree the 30amp fuse is a bad idea, I have no intent on keeping the fuse in there.
Why would it work with the stock fuse without popping when the motor is off, and only blow when the motor is running? a short is a short...right? if it blows when it's running, it should theoretically blow when it's not?

Just throwing this out if he sparks any other trouble shooting ideas.

I have a trim screw go thru my wiring harness at the driver side rear door sill. Drove me crazy since it shorted intermittently and messed with the radio and windows but no blow fuses.

that's a good pointer. door sill trim has been on and off multiple times in the past few weeks, that could be the culprit.

so it was a short in the tailgate. Drove me nuts, since It only popped the fuse when the tailgate was closed, and coincidentally I only closed the tailgate when I started the truck.
Dawned on me after I ripped out every single panel that the hatch may have been crimping a wire, when that didn't pan out, tried putting a test light on the rear hatch latch and ground, lit up instantly. One of the wires inside the hatch had the insulation completely melted off. cut the wire from power, capped it off, everything works.... I'll fix the wiring harness next weekend