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  1. #1

    Unhappy Could really use some Help!!!

    Hi everyone!
    I am new to the Forum and could really use some help. Did my first engine swap this past week and am at a standstill with an electrical issue. I was driving an 88 C1500 with a 305 in it but the body and frame just about had it, so I bought a 94 C1500 with a 4.3 that had a blown motor and the Tranny was bad, and pulled the motor. Everyone I talked to said the only thing I would have to change is the Motor Mounts and the computer and I could then put the 305 motor in. Well, that turned out to be wrong as I had to use the engine wiring harness from the 88 also, but heres the problem, I didn't realize that the plugs weren't the same where the wiring harness under the dash is, and the other truck got scrapped already. The truck starts and runs fine, but the alternator is no longer charging and was fine before the swap, and I don't know what wires go to what in the under dash harness. Can anyone give me a clue as to what each wire in the c200 connector is for on the 94, and the 88? Some of the wires in both connectors are the same color and others are different. The ones that were the same I connected together, but I am left with 4 or 5 wires on the 88 harness that don't match the 5 or 6 wires on the 94 under dash harness. I really need to get this completed and can not afford to take it to a mechanic. Do I have to get an 88 wiring harness for under the dash? And if so, will the plugs from that even fit in the 94 dash? Or will I have to replace the entire cluster panel and convenience center also? Any help would be greatly appreciated.

  2. #2
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    Welcome to the club....I'm sorry I do not have any answers for you, but there are many bright members here who I am sure will be able to give some advice.


    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

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  3. #3
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    Hate to say it, Rob, but the harness for the '88 is only used through '90. The harness is different, as is the ECM. But, don't fret yet....your best bet is to look up wiring diagrams and compare the circuits. If I am correct, I think you are going to end up with extra wires anyway. No big deal. If the ECM isn't looking for a signal then it doesn't need those. I will check some diagrams when I get home this morning and try to get back with you as soon as I can. Good luck on your hunt!
    440 HP 383 + 150 shot = fun weekend!

  4. #4

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    Thanks for getting that info to me and will be looking forward to hearing back from you. I'm attaching a couple pics of whats left over. Guess if I could figure out what each wire is for on the 94 harness, and what each one is for from the 88 I could splice together. I get kinda confused though when trying to figure out those wiring diagrams. I'm not sure if the wires that I do have connected are right or not, but they were the same colors in each harness. Don't know if the colors remained the same for each year or not. Truck does run, but keep blowing brake fuse and wipers don't work, and Speedometer doesn't work, so I'm assuming thats the leftover wires? Or maybe the color codes did change?Click image for larger version. 

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ID:	20285Click image for larger version. 

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    Quote Originally Posted by lildino383 View Post
    Hate to say it, Rob, but the harness for the '88 is only used through '90. The harness is different, as is the ECM. But, don't fret yet....your best bet is to look up wiring diagrams and compare the circuits. If I am correct, I think you are going to end up with extra wires anyway. No big deal. If the ECM isn't looking for a signal then it doesn't need those. I will check some diagrams when I get home this morning and try to get back with you as soon as I can. Good luck on your hunt!
    Last edited by roblj65; 08-30-2010 at 09:07 AM. Reason: picture size

  5. #5
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    murdog94's Avatar
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    Welcome aboard.
    I did a complete wiring harness swap from a 1992 into a 1988... All of the plugs will change over, and plug into the exsisting ECU. But if you are trying to cut and splice you will need a good set of schematics from a 1994, and a 1988.
    As for the large red wire that is the power wire for the ignition. You should have a wire under the dash that will plug in. And the large green as well. The others i honestly have no clue i would have to take a look at the remnants of the three different wiring harnesses i went thru and see when i get some time off of work..
    Mike

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  6. #6
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    Welcome,i wish i could help.I'm sure you will find help here ,good luck!
    [/SIGPIC]2009 Chevy Silverado LT 1500 EXT CAB 4X4 Vortec 4.8L SFI,K&N air filter,Weathertech Floor Liners ,Weathertech Stone/Bug Deflector, Line X Spray On Bedliner, TruXport Rollup Tonneau Cover, Molded Mudguards, Viper 5701 LE 2 way Security Alarm/Remote Starter, Xm Satelite Radio,BILSTEIN 5100 rear shocks,BILSTEIN 5100 front levelling shocks,READYLIFT 2" rear lift blocks,Goodyear Wrangler Territorys -265/70R 17"

  7. #7
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    Hi, and welcome to the site!
    Eddie , 2000 Chevy Tahoe Z71 (old style)

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