99 TJ taillight problems

[Tjman69]

Ok I’m new to this page, I have a 99 Tj, having problems with the tail lights not working. I’ve tried everything I’ve seen on here an YouTube still can’t get them to work, so what I’ve done so was checked fuses all are good besides the tail light,dash light,runner lights etc, i have a fuse that lights up when it’s blown and it’s lit up, so I tried the next thing, checked all grounds there all good, replaced the whole rear wire harness back to the tail lights and I replaced the rear tail lights, still blown fuse an don’t work but the reverse lights an turn signal work makes no sense, I’m assuming I got a pulled wire some where or a short but only other place I’m thinking is the harness behind the dash not to sure anything will help, cause if I can’t figure out this issues I’m getting rid of it, thanks.

 

[JEEPCJTJ]

A short, not necessarily a pulled wire, is what you probably have somewhere. That's when the electricity goes to ground before getting to the tail lights because the insulation is worn/cut/melted and the metal inside is rubbing anything grounded. Finding where could be as easy as sticking your head under the dashboard and seeing it or it could be as time consuming (not physically hard) as opening up the harness and spreading out the wires until you see the problem. Finding it will help. Getting rid of it, either the Jeep or the short will also help but in 2 totally different ways.

 

[Vtx531]

Is the fuse sized properly? Not too small?

You replaced the fuse with a new one after changing the tail light harness right?

The fuse blows right when you turn on the lights or it works for a while and randomly blows the fuse?

If it always blows right away...Unplug the new harness you put it, install new fuse and try turning on the lights. If it blows again, you just narrowed it down to the wiring prior to your new section (probably).

Trace the harness back visually -VERYcarefully. DONT move the harness at all until you have thoroughly inspected it. If you move it, you risk not being able to see the problem. Pay extra close attention to areas where the harness is mounted or goes through grommets, anywhere it could be rubbing on metal body. It is likely rubbing somewhere and has worn through the insulation, causing a short. Especially the case if the fuse doesn’t blow right away when you turn on the lights because it is not shorting at all times, just during certain vibration or bumps when driving.

This kind of thing can be tricky but you will feel great when you find the problem.

Have you modified the wiring at all besides installing new harness? Trailer wiring or anything at all? If so, that is a place I would start.

 

[Tjman69]

Is the fuse sized properly? Not too small?

You replaced the fuse with a new one after changing the tail light harness right?

The fuse blows right when you turn on the lights or it works for a while and randomly blows the fuse?

If it always blows right away...Unplug the new harness you put it, install new fuse and try turning on the lights. If it blows again, you just narrowed it down to the wiring prior to your new section (probably).

Trace the harness back visually -VERYcarefully. DONT move the harness at all until you have thoroughly inspected it. If you move it, you risk not being able to see the problem. Pay extra close attention to areas where the harness is mounted or goes through grommets, anywhere it could be rubbing on metal body. It is likely rubbing somewhere and has worn through the insulation, causing a short. Especially the case if the fuse doesn’t blow right away when you turn on the lights because it is not shorting at all times, just during certain vibration or bumps when driving.

This kind of thing can be tricky but you will feel great when you find the problem.

Have you modified the wiring at all besides installing new harness? Trailer wiring or anything at all? If so, that is a place I would start.

I appreciate all the help and tips from both of you guys, so to answer vtx530, I do have the proper size fuse in there, I didn’t replace the fuse that’s in there cause it’s a fuse that lights up when it’s showing it’s blown, as soon as I turn the lights on it blows an it’s lit up yellow, I never modified the harness In The rear bought it oem so it all plugged right in, I did notice I was looking at the fuse box panel behind the glove box I took it off the mounting bracket and as I would move it around that fuse that was blown would go out an then come back on as of like when I move it around the wire might be not rubbing an getting power or could be grounding itself, my next step as of right now I’m going to take some of the dash apart an inspect the harness up front to see if I fine any broken wires or what not.

 

[Tjman69]

A short, not necessarily a pulled wire, is what you probably have somewhere. That's when the electricity goes to ground before getting to the tail lights because the insulation is worn/cut/melted and the metal inside is rubbing anything grounded. Finding where could be as easy as sticking your head under the dashboard and seeing it or it could be as time consuming (not physically hard) as opening up the harness and spreading out the wires until you see the problem. Finding it will help. Getting rid of it, either the Jeep or the short will also help but in 2 totally different ways.

Thanks for the help, I’m thinking it’s a pulled wire or one that’s grounding it’s self behind the dash, cause the rear harness is new as well as the lights, gona try an inspect them after I pull some of the dash off an will get back to you.

 

[Vtx531]

What is the harness that you replaced? Including the one that goes from right to left for the tail lights? Check the third brake light wiring as well

 

[Tjman69]

What is the harness that you replaced? Including the one that goes from right to left for the tail lights? Check the third brake light wiring as well

I replaced the harness from where it plugs under the dash all the way back to the tail lights that whole section as well as new tail lights, also what is the third brake light wiring would that be the trailer brakes?

 

[Jerry Bransford]

Do you have a "protective" tail light cover installed over your tail lights? If so, those useless things are notorious for causing electrical issues due to them screwing with the proper grounding of the tail light assembly.

 

[T Crawford]

You might look at your multifunction switch wires, I think the brake wires may pass through there, recently my 06 had light problems and I replaced the harness plug that went into the multifunction switch and that solved it. Get a Mopar plug if that is it, it solved my problens

 

[Tjman69]

Do you have a "protective" tail light cover installed over your tail lights? If so, those useless things are notorious for causing electrical issues due to them screwing with the proper grounding of the tail light assembly.

Yeah I do but it’s all brand new it’s gotta be a wire in the harness in the dash is what I’m thinking

You might look at your multifunction switch wires, I think the brake wires may pass through there, recently my 06 had light problems and I replaced the harness plug that went into the multifunction switch and that solved it. Get a Mopar plug if that is it, it solved my problens

witch plug?

 

[JEEPCJTJ]

Do you have a "protective" tail light cover installed over your tail lights? If so, those useless things are notorious for causing electrical issues due to them screwing with the proper grounding of the tail light assembly.

Yeah I do but it’s all brand new it’s gotta be a wire in the harness in the dash is what I’m thinking

It wouldn't be a bad idea to double check the harness back there.

My wife bought those for me for Father's day 2018 and I put them on. I made sure to add Fluid Film where they touch the body and the tail lights to keep rust away from where I roughed up the paint around the holes to make sure my ground was good. IIRC, what I liked the least about them was that the hole for the wiring didn't completely line up with the same whole in the body. I don't remember if I had to open those holes up somewhat or not but I do remember wrapping those wires in a few layers of electrical tape just to make sure they would never get shorted there.

 

[Jerry Bransford]

Yeah I do but it’s all brand new it’s gotta be a wire in the harness in the dash is what I’m thinking

Again, those tail light covers are 'notorious' for causing that problem. Brand-new or not. The tail lights get their electrical ground connection through their mechanical connection to the Jeep, not through the wiring harness. Those "protective" covers can get in the way of that ground connection. Which is why I asked you if you had those covers installed, I would have bet $$$ you did from the symptoms. Believe me or not.

 

[Vtx531]

Here’s some encouragement for you. This is from today on my daily driver 2013 Ford Fusion PHEV.

I was able to find a broken wire located inside the loom. The only clue was the plastic loom was worn in a spot. It was rubbing/vibrating on the bolt head, wore through the plastic loom, through the wire insulation, and was probably like like for a long time until corrosion finished it off and completely broke the wire. Only way to find it cut the tape off the loom and peel it back until you find the problem.

Third broken wire I’ve had on this car! It was not a power wire so no fuse blown (PWM signal wire) but I had a similar issue on a power wire for one of the battery cooling fans and it caused the fuse to blow intermittently from shorting out. The other one I had issue with was a speed sensor wire so no blown fuse there either.

 

[JPHikr]

First question is do you own an Ohmmeter?
https://wranglertjforum.com/attachments/1999-tj-service-manual-pdf.14034/
Start on page 553.
Check your ground first, then check for power at each light.