Blowing the taillight fuse?

I have a problem with my fuse for my taillights blowing whenever I turn on my headlights. I initially thought it was the headlight switch so I replaced that, but it still isn't working.

My dash lights don't work either.

Any other suggestions on things to check? Both my taillight bulbs are fine since they come on when I hit the brakes, so I know they're not burnt out.

The tail light bulb element is different from the brake light element. Take the bulbs out, turn the headlights on, and see if it still blows the fuse. Or use an ohmeter to check the bulbs for correct resistance. Do you have trailer light wiring?

Yes I do have trailer lights, and they are working fine. No fuses blown on their circuit.

I'll check the brakelight bulbs next I guess.

I don't understand. The trailer lights are on the same fuse circuit as the vehicle lights. If your tail light fuse blows for the XJ, it also blows for the trailer.

Sorry, I should have been clearer... the trailer lights are on the same circuit as the taillights. BUT they have their own inline fuse where my trailer lights tap off the taillight lines. That fuse is rated lower then my taillight fuse so if there's a problem with the trailer lights, it should pop that fuse before it pops the taillight fuse.

So right now with the taillight fuse popping, my trailer lights don't work either, but I am quite sure they're not the problem since their fuse is still fine.

Ok so I still have a problem here... I have been checking things out one at a time and I have had no luck.

So far I have replaced:
Headlight switch
Headlight bulbs
Taillight bulbs/Rear signals/reverse lights

I have unplugged my trailer brake controller up front and also the whole tow package at the rear has been pulled out.

I am still popping fuses as soon as I turn my headlights on.

Any ideas on what else to check? I don't know what all that stupid 20A fuse feeds so I have no idea what to keep looking for. I am going to pull the dahs apart and start checking bulbs there pretty quick but I kinda think it's a last ditch effort since a burnt out bulb normally shouldn't make a short...

Does it do it when parking lights or headlights? Dash lights should come on with parking lights

I don't know the circuits but if it were me going blind I would disconnect the headlights and see if it still tripped.

When I pull the switch out 1 position it blows, so I guess parking lights.

I have headlights... I just don't have dash lights or taillights. I have brakelights and turn signals and hazards still but it's getting ridiculous driving on the highway at night with my hazards on the whole way home...

Pull the instrument light fuse, the power for instrument lights goes through the parking light fuse first (on many early to mid models). It may be your problem, especially if somebody put too big a fuse in the instrument light fuse socket. I had a short in the harness, between the fuse panel and the dash lights. Your transfer illum (clock and other stuff) is also on that circuit, the wire bundle under the drivers side carpet is a likely spot for a short.

I did a little more poking around:

I found my license plate light bulb was burnt out so I replaced it.
It didn't help.

I pulled the dash light fuse.
It didn't help.

I pulled almost every fuse I could see that could be related to it (high beam fuses, low beam fuses, dash lights, trailer package etc...) and I'm still popping that stupid 20A fuse under the hood!

This is getting to be very frustrating. Any other ideas on things to check?

Did you try taking out all the bulbs on that circuit? License plate tail lights, front and side parking lights and see if the fuse blows? It probably will. Then you know it's the wiring somewhere. You haven't said anything yet about checking with a multimeter. That is the way to trace shorts.

I'll pull all the bulbs and try again.

I checked right at the fuse with a multimeter... I'm not sure which side of the fuse is the hot coming from the battery and which one goes to the circuit but I checked both sides to ground (separately) and found no continuity so I don't think it's a wiring short... just an overload of some sort. But I could be wrong. I'll try it all again with the bulbs out and see what happens.

Well I finally got it figured out today... it turns out a lot of that stuff isn't off that 20A circuit in the PDC. That circuit really only has a couple things on it:

Fuse 6 in the interior fuse block
Fuse 7 in the interior fuse block
An illumination wire for the factory radio

Because both fuses 6 and 7 were fine on my jeep, that means that the problem is somewhere before the power got to those fuses.

But since it only happened when the headlight switch was turned on, that means that the wiring from the 20A (in the PDC) up to the headlight switch, was fine and that the problem was somewhere between the headlight switch and those fuses.

That only leaves a little bit of wire to check out with the multimeter... and when I found no shorts in those 2 sections of wire I knew the problem had to be the radio illumination wire that came off the headlight switch.

The FSM showed the radio illumination wire to be Black and Yellow so I pulled the dash apart at the radio to find that wire.

A little more poking around and I found that the wire had been pinched from when I was doing some work on my dash and it was shorting out. A little heat shrink and a butt-splice fixed the problem nicely and everything is working great again.


I am attaching a diagram I made of that circuit for future reference for anyone who is having a similar problem.

Circuit F34 is that 20A fuse in the PDC.
The rest should all be pretty self-explanatory.

glad you got it figured out