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1999 XJ Classic - melted wiring harness...

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Old 08-11-2017, 06:58 PM   #1
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Default 1999 XJ Classic - melted wiring harness...

Sorry - just noticed I posted on wrong forum... Moved to correct forum.


Hoping to get some help here... My son has a 1999 XJ Classic and CEL came on the other day. Popped the hood and notice that the plastic wiring rail harness that runs along the valve cover was melted - along with the wires running through it... See attached pictures. Obviously need to replace the rail and wiring but not sure if the wiring harness is completely replaceable as a single unit...

Any help or guidance here would be much appreciated. Not sure what caused the plastic rail to melt. The jeep is running fine but expect that the melted wiring to the fuel injectors will be an issue soon if we don't get this replaced.

Thanks for any help.
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Last edited by tb24; 08-11-2017 at 07:33 PM. Reason: Wrong Forum - reposted on correct one.
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Old 08-12-2017, 02:54 AM   #2
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Wow. First you need to figure out how that happened. No sense in fixing that if it could happen again. I know on a '00, cause I pulled one out of a boneyard Jeep, that the fuel injector wiring is a small part of the bigger harness. Consists of almost everything starting with two out of the three connectors that go into the computer, running around the firewall, with everything from the O2 sensor connectors, grounds on the passenger side of the engine, and pretty much everything also on that side. Kinda of a pain to remove with the engine and tranny in place. Figure even harder to put in. Thinking it would be easier to rewire just what you have too. If you do decide to replace the whole harness with boneyard parts my guess is that you should try to stick with '99. Will want the donor vehicle to be the same emissions that you have. Federal or CA. Also have the same tranny. Stick or automatic. Thinking '97 or '98 would most likely work as long as the other stuff is identical. '00 and and '01 will not.
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Old 08-12-2017, 06:00 PM   #3
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Wow. First you need to figure out how that happened. No sense in fixing that if it could happen again.
Agreed! Looks like you had a small fire there. Perhaps an injector is leaking a tiny bit of fuel, and it ignited?

If you decide to splice in new wiring (probably the easiest route), don't go cheap. Buy nylon butt connectors with the built in sealant, and a decent quality crimper, or even a good crimper. Do NOT buy some kit of connectors that comes with a stamped metal crimper, like this junk.

And don't let anyone tell you that soldering is better. Not true. Properly done crimps are better, faster, and easier. They are preferred in marine applications, for example, while soldering is permitted.
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Old 08-13-2017, 01:33 AM   #4
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Thanks - agreed that replacing only what I need would be easiest but the harness running through the plastic rail is completely melted. Would be great to get at least that section of the harness and splice it in...

Either way it doesn't look to be simple fix.

Appreciate the help/advice.
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Old 08-13-2017, 02:17 AM   #5
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Thanks - agreed that replacing only what I need would be easiest but the harness running through the plastic rail is completely melted. Would be great to get at least that section of the harness and splice it in...

Either way it doesn't look to be simple fix.

Appreciate the help/advice.
That is probably a good idea. Did not think of that. As I stated before pulling the whole harness that the fuel injector connectors are on was a pain. But getting just that part would probably be pretty easy and not that bad as far as installing. Also thinking it would improve your chances of finding what you need. Thinking maybe you could use one from '97 to '01 and might not care about Federal or CA emssions, auto or stick. Guess it will depend how much of the harness is fried.
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Old 08-13-2017, 05:47 AM   #6
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A trip to a pull-a-part place with a good pair of side cutters should get you what you need.

But you still need to fix whatever caused that!
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Old 08-13-2017, 09:00 AM   #7
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A while back Cruiser54 posted a thread pointing to an area of that harness thats vulnerable to shorting or open wires.
Its where that harness enters the channel near the firewall.
I tried a search for that thread but no luck, you might have better luck.

Before going to the bone yard try to find that thread, you might need to cut off as much of the donor harness as possible just in case.

I had something similar with my old '94 XJ but not as severe. Must of caught it in time.
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Old 08-13-2017, 10:10 AM   #8
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Not sure what caused the plastic rail to melt.
That's a fire, most likely from a fuel leak.

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The jeep is running fine but expect that the melted wiring to the fuel injectors will be an issue soon if we don't get this replaced.
You're going to need to replace the damaged injectors also. Might as well do them all while you're at it. Given that they crack open by themselves over time, I seriously would not try to run injectors damaged by fire.

Personally, I'd take this opportunity to upgrade to 4 hole or 12 hole injectors. But that's just me.

Can you solder? I really wouldn't use butt splices on the injector harness if I were you.
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Old 08-13-2017, 11:19 AM   #9
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That's a fire, most likely from a fuel leak.


Can you solder? I really wouldn't use butt splices on the injector harness if I were you.
You guys really think that's from a fire? I suspected the plastic railing failed and got too close to the engine. Live down here in Texas and it is extremely hot...

If it was from a fire - that plastic would not have stopped burning... but that's just my assumption.

I can solder - that seems like an extremely difficult area to have to solder all those splices back together. Since, if using a replacement harness, it would be spliced on the back side of the engine. I would think soldering would be a much better connection but will take a look at the heat shrink/butt connectors - that looks like it could work. Would be a lot of butt connectors and quite bulky with all the wires.
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Old 08-13-2017, 12:28 PM   #10
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You guys really think that's from a fire? I suspected the plastic railing failed and got too close to the engine. Live down here in Texas and it is extremely hot...
That's high temperature plastic. It's not usually going to melt just from being too close to the valve cover.

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I would think soldering would be a much better connection but will take a look at the heat shrink/butt connectors - that looks like it could work. Would be a lot of butt connectors and quite bulky with all the wires.
I hope you didn't misread what I wrote above. I would NOT use butt splices. If you can solder, take the time to do it right with soldered joints covered with heat shrink tubing.
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Old 08-13-2017, 12:36 PM   #11
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Wiring doesnt melt like that from a hot day. Neither does plastic. Think bigger.

High resistance for example builds heat. That resistance keeps building and the heat gets hotter and hotter. Wiring cooks from that heat and the insulation starts to melt, which then burns, and then catches fire. Shorted wiring will do the exact same thing. Hopefully the fuses protecting those circuits popped and that damage is all there is. That harness is replaceable but youre going to need a parts yard, a used harness online, or post a wanted ad. That harness snakes along the firewall back to the PCM and, IIRC, there are quite a few splices along the way. You have a lot of work ahead of you. Not just in repairs, but why it burned in the first place.

Crimp or solder, thats up to you. Both will work, and last, if done properly. If you do solder, use Rosin core only for automotive applications. Solder takes practice. If you crimp, stagger all connections (with heatshrink tubing). These are also an option. All you need is a heat gun.


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Old 08-13-2017, 02:39 PM   #12
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Can you solder? I really wouldn't use butt splices on the injector harness if I were you.
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I hope you didn't misread what I wrote above. I would NOT use butt splices. If you can solder, take the time to do it right with soldered joints covered with heat shrink tubing.

For joining wires, soldering is inferior to correctly done butt splices. That's why it's spec'ed in a lot of places where soldering is not permitted (many military and aerospace applications), and preferred in other places where soldering is merely permitted (civilian marine applications).

Use quality materials and tools, and a butt splice will outperform a solder joint every time.

And yes, stagger them, or you'll have a big lump to deal with!

Those Monolit connectors are new to me, so I have no comment on them. They look pretty good, but I have not seen any studies on them. "Easy to use" does not always equate to "good to use".
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Old 08-13-2017, 04:13 PM   #13
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...

I'm reconsidering.

...

And now after reading for a while, I really don't think it matters which one you use as long as you use the right tools and do it correctly.

Last edited by extrashaky; 08-13-2017 at 04:58 PM.
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Old 08-13-2017, 06:05 PM   #14
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Old 08-14-2017, 05:10 PM   #15
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Wiring doesnt melt like that from a hot day. Neither does plastic. Think bigger.

High resistance for example builds heat. That resistance keeps building and the heat gets hotter and hotter. Wiring cooks from that heat and the insulation starts to melt, which then burns, and then catches fire. Shorted wiring will do the exact same thing. Hopefully the fuses protecting those circuits popped and that damage is all there is. That harness is replaceable but youre going to need a parts yard, a used harness online, or post a wanted ad. That harness snakes along the firewall back to the PCM and, IIRC, there are quite a few splices along the way. You have a lot of work ahead of you. Not just in repairs, but why it burned in the first place.
While I would agree with most of what you said. The symptoms are not what you would expect from a fire and/or shorted wiring. The truck is running fine - nothing shorted out and no fuses popped. I just have melted mess along that plastic rail and just in the center...

Regardless, I totally agree - it will be a lot of work. Just still trying to figure out what caused it to begin with.

Thanks again for all the input.
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