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Old 04-20-2017, 12:12 PM
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Can't get headlights or running lights to work..

So I have a 1986 gmc k2500 p/u that used to be a diesel but now its got a crate 5.7l. I took all the original wiring out of the engine bay that went no where or to sensors that didn't exist anymore. Since then My headlamps wont light. I used a dvom to figure out which terminals on the underhood fuse block that gives the whole system power as well as the one that provides power for the hei/starter solenoid. I checked the underhood fuse block connections for the lights as well as the dimmer switch under the dash and none of the terminals have power. My rear running lights also do not work but reverse, brake, and turn signals all around work. I can rewire the lights myself with a custom switch which would be nice but I would like to have the original switch working as this is kinda a restore project. I am really at a loss because it seems the diesels were wired differently than gas versions and I cant find an accurate diagram of the fuse block or even mentions of the underhood pinout. What can I do?

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Old 04-20-2017, 12:31 PM
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I would suggest getting diagrams for both diesel and non diesel to determine what the differences are.
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Old 04-20-2017, 04:45 PM
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Well.. I found something out. I hooked up my ect 2000 gnd/open circuit finder and attached it to the lowbeam side under the hood. The connector harness that goes from the dimmer switch to above the steering column under the dash has a problem. If I wiggle the harness my device will go back and forth from open to not open. I don't know if I want to tear apart the dash and column just to get to it. I already had to replace the ignition switch on top of the column on my s10 and it took me days. Perhaps building my own circuit and switch will be easier..
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Old 04-21-2017, 05:27 AM
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The forward lamp harness is completely separate from the engine harness on these trucks. There is no need to "completely rip it out."
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Old 05-01-2017, 05:41 AM
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No miracle cure here, patience is the key... Do continuity tests on each wire. Remember that since both front and rear lights do not work, the problem is between switch and power source, that is less wiring to check!
You have probably damaged a wire/connector during the engine swap...
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