Brake/Signal Light Problems

[fony3]

So for a while now I've been having troubles with my rear right tail light. When the headlights are off the right signal and brake work fine. As soon as I turn the lights on, the running lights work, but when i signal (and the fast signal click indicating a burnt out light) or brake the light turns off.

I have checked the bulb, and it seems to be working fine. Now from reading about similar issues it seems it could be a flasher relay or a multifunction switch box.

Where should I start? Is there any way to test these modules or is it basically buy and replace troubleshooting.

Thanks

[Tinkerer]

First thing I'd suspect is a bad ground myself, especially since it works fine with the headlights off. It sounds like it is grounding through the other filament when the lights are off, but when they are on, that route to ground is gone and it doesn't work.

If I were going to swap anything, I'd be putting another load on there like another bulb done up to say a trailer wiring harness or something to load test the circuit with a known good ground, probably the cheapest, most accessible thing to start with.

[fony3]

Ok, I dont have a trailer harness, whats an easy way to do that?

[Tinkerer]

Ok, I dont have a trailer harness, whats an easy way to do that?

I bought a trailer wiring harness from Canuck Tire for cheap... and had trailer wiring as a end result   If one is adventurous and saving money as all us Jeeper$ have to do, just stick wires into the sockets where the wiring harnesses connect. The trailer wiring harness just "T" connects into the factory harness at an existing connection behind the tail lights.

Where are you? I am in what was the extreme NE (not so much anymore) in Taradale if you want me to find time to have a look.

[fony3]

beauty, thanks for the info, I'll start by playing just with that harness where the trailer harness plugs in. Thanks for the info, hopefully I figure out the problem.

[specialk]

I had a similar problem.  The owner before me towed the rig and had some nifty splitters inline with the wires to the tail lights.   Found they were causing my problems.  You can get at all those connections behind the drivers sire rear tire and test the different combos.  I had to do some minor re-wiring back there to make everything work with the trail harness too.

[Elsifer]

I would rule out the ground issue first, as it's most likely.

The flasher module is just that a flasher, it flashes the same on right or left. At least on the 03/04 and newer TJ's. So likely a ground, especially, when the function changes (your lights come on). Prolly a chafed wire behind that lamp. Or not far from it in the harness.
But the flasher is a pluggable module (depending on your year of heep), and I recall, its about $20, I went thru one when I did my LED lights, and I had to mod the new one so it wouldn't fast-flash like a bulb was out.

You could try with a multimeter to map out the functions of the various wires behind the one that works, then try on the one that doesn't. that will at least lead you to a bad wire, then finding the fault will be fun.

But a trailer harness makes things easy, especially if it T's into existing wiring, a trailer light tester will give you a fault which you can trace.

Wiring, its like a pipe, but smaller and bendy!

[Rookie]

Do you have the right bulb in there  it should be an 1157 dual filament bulb ?
Switch the bulbs side to side  and see if the problem changes sides as well, it could be the filaments are shorted internally the signal and the brake use one filament and the marker uses the other.

I'd bet its the bulb 

Steve