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Old 07-02-2017, 03:35 PM   #1
c20pickup
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Join Date: Apr 2013
Location: Brighton, WI
Posts: 504
weird electrical issue

in finishing my 70 c20 i purchased a complete electrical harness, front to back, engine, interior, the whole 9 yards from classic heartbeat. 90% was plug and play, which is excellent. anyway when i receieved the kit it consisted half of M&H wiring and half of American Autowire (i believe thats who's it was) i contacted wes and he said the two harness are identical and work together, which they did, i just wanted to clarify what im working with here.

so here lies the issue.. everything with the engine, dash cluster and interior work as normal (havent hooked up the radio or blower/heater box yet). but my guages, tachometer (factory tach) dome light all work normal. however with the battery hooked up and the headlight switch off, my driver front marker light in the fender stays on, and my tailights stay on, everything else is off as it should be. when i pull the switch halfway out to activate just the clearance/parking lights all the lights come on as they should but the front driver marker in the fender now goes dead and the passenger blinker in the grille is illuminated but very dim, driver side blinker in the grille lights up nice and bright. i go further and turn the headlight on, headlights do come on but still same issue as before, driver marker is dead and passenger blinker is dim.
its almost as if something is backfeeding to the driver marker? i dont know and im not sure where to even begin looking.

next issue is no turn signals. the passenger turn signal works intermittently when the headlights are on but driver side never works (bad connection, bad flasher???) i reused my old flashers from my old harness, not sure if they could go bad from sitting?

no brake lights either. i have the pressure switch on the master hooked up and i cleaned the post with some fine sand paper and the two prong switch under the dash is hooked up, still no brake lights.

i should mention that all the above issues are not affected with the key being on or off.
i have ground straps going from the body to the frame, engine to the frame, and engine to the body. i can check anywhere thats bare metal, aluminum and both sides of my ground straps with a power probe and have a good ground connection.
the truck has an aftermarket steering column and i bought the harness that converts the aftermarket blade style connector to the factory half moon style, before plugging it in i made sure all the wires lined up and all the colors corresponded and they did, much to my surprise.

sorry for the long winded post but any advice where to start looking would be great!!
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Old 07-02-2017, 04:19 PM   #2
toolboxchev
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Re: weird electrical issue

Look into everything that ties into the steering column. Most all rear brake light issues trace back to there and the turn signal cam switch.
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Old 07-02-2017, 09:02 PM   #3
LockDoc
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Re: weird electrical issue

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Also read this thread and check all of your ground straps. It's three pages but it is a good read, and very important.....

http://67-72chevytrucks.com/vboard/s...d.php?t=422234

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http://67-72chevytrucks.com/vboard/s...d.php?t=829820

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