New LMC Wiring Harness Issue - Need Assistance!

[AF-s10]

Hi all! It has been a while, I have kept mostly to mys10 while I have been working on my truck.



I am in a bind, and direly need help from an automotive electrical expert. I bought a replacement wiring harness from LMC for my 86 GMC Jimmy. I got the kit in, but it is definitely not a direct fit plug and play replacement. It is a stock 6 cylinder, not sure the size off the top of my head. The new harness has no connectivity for the ECM. Talking to one of the guys here at work, he was saying that an ECM was not needed for a carbed engine. Is this true? I ran into a problem of zero running capability, and opted to get a new harness, instead of getting a replacement from a junkyard.



I can't return the harness I have, because it is out of the box already. I have to figure out how to make this kit work, otherwise I am out almost 500.00, and still at square one without a running truck.



Can anyone provide any insight on this? I am by no means an expert, but I can usually pick up pretty quick. I don't have anyone local I know who can help me out, so I am hoping someone on here is an expert that might be able to walk me through this, if it is possible.



Thanks everyone!

[355V8S10Tahoe]

On 2008-02-11 12:38, AF-s10 wrote:

Hi all! It has been a while, I have kept mostly to mys10 while I have been working on my truck.



I am in a bind, and direly need help from an automotive electrical expert. I bought a replacement wiring harness from LMC for my 86 GMC Jimmy. I got the kit in, but it is definitely not a direct fit plug and play replacement. It is a stock 6 cylinder, not sure the size off the top of my head. The new harness has no connectivity for the ECM. Talking to one of the guys here at work, he was saying that an ECM was not needed for a carbed engine. Is this true? I ran into a problem of zero running capability, and opted to get a new harness, instead of getting a replacement from a junkyard.



I can't return the harness I have, because it is out of the box already. I have to figure out how to make this kit work, otherwise I am out almost 500.00, and still at square one without a running truck.



Can anyone provide any insight on this? I am by no means an expert, but I can usually pick up pretty quick. I don't have anyone local I know who can help me out, so I am hoping someone on here is an expert that might be able to walk me through this, if it is possible.



Thanks everyone!







First of all I think an 86 would be a 2.8L V6 and TBI with an ECM, I think the kit you got from LMC is a universal kit intended for use with a carbed engine, not an OEM replacement that has ECM circuits... I've never seen an OEM replacement wire harness in the LMC Truck catalog, only the universal kit and some heavy duty relay wiring add ons for headlights, cooling fans and stuff...



What do you mean by: zero running capability?



Why do you think you need a new wire harness?



If the wire harness is not burned up or something, maybe we could just help you diagnose why it is not running, it could be many things and more detailed information is needed...



Does it actually have a carburetor?



I presume it is TBI, I would check fuel pump function first, does it prime when you turn the key on? Can you hear the pump in the gas tank run? It only does this a second or two when priming... You can also test run the pump by jumping a wire from the power block on the firewall to the pump prime wire that hangs down next to the power block, it should be a tan with white line wire that connects to nothing...



Good luck, I hope I helped a little... http://www.s10v8.com/images/smilies/icon_confused.gif

[AF-s10]

Primary problem was a series of shorts and disconnects, including a slow battery drain. had someone take a look, and was told best bet would be to replace the engine side wiring harness. Unfortunately, I did not realize the universal harness would not work. I bought the kit, and the old harness is out of the truck now. So I am in a spot where I need to figure out how to make the new harness work, or put the old harness back in, and still have the same problems, and be out almost 500.00. I am stuck between a rock and a hard place at this point.

[355V8S10Tahoe]

Well, that sounds like a real bummer... All I can suggest is to try selling the universal harness someplace like E-bay to try to recoup some money and hit a junk yard for a decent engine bay wire harness that fits the truck... Maybe someone else on this forum has a better idea?



I'm just wondering what series of shorts happened and what series of things caused these shorts, they may need to be replaced or repaired also??? In the event that the shorts may have damaged the ECM or other parts of the engine management system, I would be looking at getting these parts along with the wire harness as a complete assembly just to be safe, but then again if I had it I would probably convert it to a carb and get a distributor from an 82 to 85 S10, get rid of the computer and install a low pressure fuel pump.....but then that's if I didn't just convert it to a V8, it is a perfect candidate you know........http://www.s10v8.com/images/smilies/icon_biggrin.gif

[AF-s10]

What all would be required to swap it to carbed? I think that would be the easiest option, then I can use the harness, with minimal additions....



I almost would rather carbed anyways, at least those can be worked on, and eliminating the wiring disaster from the ECM would be a treat



I wish I could afford a v8, but right now I am just trying to get running.

[AF-s10]

Oh, I kept forgetting about the problems I was having.



It started out with a short that was killing all my turn signals. I replaced the turn signal switch, and it was working sort of.



I added aux. lights, and suddenly my headlights and signals were working, sometimes.



After that, I lost something else, oh, I think the door sensors decided to come on at 2 in the morning for no reason, and kill the battery.



I replaced the battery, and even with spray into the carb, it would only run for about 2 seconds. Had Rudedogg come over and take a look, and realized half the engine wires were spliced, eaten through, or somehow repaired.



I know I am missing something....oh, one of the 12v power wires was eaten through, but ran behind the block near the firewall, and somehow did not have another end...

[bassic1967]

sounds like ground wires are cut, spliced corroded, etc.. go to the local junkyard and get the wiring harness you need, make sure it is the same engine,trans, and fuel combination.

most junkyards cut the engine harness when they pull an engine out so look for a truck with the engine still in it. put your other harness on ebay for sale, someone else who needs that harness will snap it up to save $50 over the new price. computers are very touchy when it comes to resistance variations in wiring, and every time a wire is cut and spliced it changes the resistance in that wire.