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Tail Light Splice Circuits?


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So I recently rebuilt my tail light harness(connected all the right wires, soldered, and heat wrapped) so I could have it all fixed and working. The issue, however, is that because the prior owner/builder(I use that term lightly) did an engine/cab harness splice that was connected in all the wrong spots. I reconnected the ones I needed using a multimeter to see which was which and now I have turn signals and stop lights in all the right places. The issue I run into is that now I don't have any nighttime running lights(lights that come on when the headlights are on), which I found were on a separate wire that I verified with the multimeter. There's only, at most, 3 wires going into each light, so my question is, can I hook 2 live wires into the same circuit without overloading it? I'm not entirely sure how it used to function(I feel like there was a multifunction switch for it) but now it's either sacrificing the turn signals, stop lights, or the running lights. If I can't connect 2 wires to it, is there some kind of hub I can buy to connect them at lower capacity?

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I mean I only have 3 available wires running to the tail lights. But in order to have night running lights, there is a 4th wire. So I'm asking if it is possible to have the live running lights and the stop light or signal lights on the same circuit, attached to a single wire. There would be 2 live wires attached to one wire running to the lights. I'm not sure if that would blow a fuse or bulbs or just be a hazard.

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So, from what I can tell I should have 2 wires (one for right one for left) coming from my turn/hazard/stop light switch or relay(not really clear on which I should have). Instead, I have 4 wires each separated out for stop, turn right, turn left, and hazard, that are live respective to whichever operation is functioning. I'm not entirely sure where to go next for this, as I'm either missing a critical component that I'm not sure exists, or what I have is so mangled, electrically, that it just isn't working as intended. I'll try to pry more into finding where the wires go today. Do post renix era comanche and cherokees (since this was a 94 swap) have a relay or multifunction switch dedicated to meting out the activation of the wires? 

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  • 2 weeks later...

Back again with some more info since I've been spending all my time trying to fix this issue. Here's what more I know:

 

I purchased a tail light wire converter(for trailer wiring) to throw in the linkage (finally found that on a hot rod forum) that effectively turn my 4 wire system into a 3 wire. Seems simple. Just wire it in how they say to and all should work. I've been through 2 different companies now, and both have the same issue. I  can hook up all the necessary wires to each other, but it won't get a signal through. When checking with a multimeter, it shows there is no signal coming out of the box. Nothing was making it through. When I checked the input side, though, the turn signal that should have been active on one wire was active on all 3(stop, right, left). So the signal is backfeeding or crossing to the other input wires. This happened with the 4 to 3 wire converter and (I purchased a 3 to 2 wire one since it's only really the turn/stop I need to fix) the same results with the smaller one. I've scrutinized wiring for days and can't get this to work. I don't know why these boxes aren't doing what they're supposed to. 

 

On an interesting side note, which may be of help, when I have the 4 to 3 hooked up, I can get the turn signals to work if the Stop light input wire is connected to either end of the running lights wire(both input and output, even when they aren't connected). No idea why it does, but it does. 

 

My best guess here is a ground on the brake wire circuit? But when it's all hard wired together(turn signals for each side and stop wired to the running light line) it works fine, just no running lights, so wouldn't the symptoms repeat?

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When Hornbrod posted the link to the '88 electrical manual, you were trying to figure out where the three wires from under the dash meet up to feed the bulbs. Then you apparently gave up on that and tried an aftermarket converter. How much of the late-model Cherokee harness did the previous owner splice in? Was it just the engine harness, or did he also include the dash harness?

 

And do you know what year Cherokee the "new" harness came from?

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I have a set of wires that bundle and go towards the back(my fuel pump set, tail lights, basically anything rear electrical) that have the leads to the tail. The wires under the dash that are the source are part of a huge bundle. I ran multimeter tests to determine which was which. When I first posted, I thought it was less about the incompatibility of the wires and more that it's just a mess of connections, but now, it's very clearly a wire setup for a Cherokee vs. the Comanche.

 

It was from a 94(they said. I'm inclined to believe it for the most part because of other items the engine has). And as far as how much, it's really hard to tell. It's a hack job under there. Even the engine bay was a spliced together wreck. So, as far as I can tell, both the engine and the cab are spliced harnesses.

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This may help -- or may not.

 

ALL XJ Cherokees were set up with separate brake lights (red) and turn signal/hazards (amber). That held true from 1984 right through to the end, in 2001. However, the XJ Wagoneers had all red tailights, and the brakes, turn signals, and hazards all shared the same bulbs -- just like the Comanche. The problem people encounter in splicing a Chrrokee front harness to the rear chassis harness of a Comanche is getting the rear lights to work properly -- exactly what you're encountering.

 

I think the answer is to be found in the '88 electrical manuals. Hornbrod gave you the link to the MJ manual. Find the schematic in there for the MJ taillight wiring. Somewhere on the Internet, the '88 XJ electrical manual is also available on-line. Find that -- there should be two taillight diagrams, one for the XJ Cherokee and one for the XJ Wagoneer. They are different. Study where they are different, compare to the MJ diagram, and you should be able to solve the problem.

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