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Old 09-19-2017, 02:43 AM   #1
ace347
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Lightbulb ground issues and general wiring help

Here's the combo: I bought a 71 c20, mostly complete minus the engine. Over the past two years I've installed a 07 6.0l truck motor with the original granny 4 speed and replaced some of wiring if not tried to fix the rest. I almost have it road worthy (perhaps not technically road legal).

More specifics on wiring situation: The headlight harness is all new, because of farmer john butchery, courtesy of LCM. I took the engine harness off. I pulled out the dash harness and went through it, deeming it worthy of re-installation since there wasn't any splices or rats nest. The chassis wires that go back to the rear is original except for a patch or two. The tail light harness is new as-well. The gauge cluster is in-tact and I got all the gauges to work ('cept speedo cause cable and all). I am missing the wiper switch(plan to take care of that tho). all the bulbs, fuses and blinker switches are new and they all seem to work in some way shape or form. (no bulbs in rear markers yet). No fuel tank wiring(removed in-cab tank). No interior lights aside from dash lights.

The symptoms: When I turn on the running lights the passenger front side marker does not light up. With the lights on, the passenger tail lights works great but the driver tail light is dim and when you step on brake it turns off completely. When the lights are off the tail lights work as they are supposed to but the driver stop light is very dim. The blinkers do not work by them selves but the hazards work just fine, even the pass front marker blinks. The gauge lights don't work when the lights are on. The e-brake light comes on when cranking the motor but not when the e-brake is actually utilized. The turn indicators on the dash come on with-out blinking only when hazards are engaged. I have one mystery plug under the dash that I assume is to the missing wiper switch(three prong in the shape of a mostly flattened L). The back-up lights don't work yet 'cause the reverse switch pigtail goes through the engine harness.

I understand that there is a ground issue somewhere but I'm not sure were to start looking. I'm a novice at best when it comes to diagnosing these problems and a multi-meter is Greek to me. I found diagrams but can't figure out what I may have missed.

My question is if the main fuse box ground is on the engine harness that I excluded. I would appreciate any tips or tricks you can give me.
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Old 09-19-2017, 08:09 AM   #2
notsolo
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Re: ground issues and general wiring help

You have probably done this, start under cab, clean frame and ground strap area on cab new star washers might help, move on to front end and frame, motor to battery etc. Good luck.....Welcome aboard also.
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Old 09-19-2017, 09:05 PM   #3
68c10airstream
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Re: ground issues and general wiring help

Take a look at the right hand inner fender on the underside up front. I think a braided strap goes from inner fender to frame rail on passenger side. Obviously the engine is grounded because the starter works ok, the cab is on rubber mounts and that it grounded from braided straps from the heads or valve cover bolts to the firewall. I've changed my battery location but i think a ground went from the battery cable at the battery to the rh side fender. So look all over the frame for a braided strap, but i think my 68 c10 is as mentioned. Good luck!
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Old 09-20-2017, 10:40 AM   #4
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Re: ground issues and general wiring help

I had to ground my bed to the frame to make my marker and tail lights work correctly. One other thing is to make sure the tag light wire is not broken and grounded to the frame.
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Old 09-20-2017, 12:08 PM   #5
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Re: ground issues and general wiring help

You have too many problems to just start groping through the wiring harness blindly. You will have to learn the circuits and what the different colored wires do.
Above all you need to get yourself an multimeter and learn how to use it.
Here is a very good tutorial from U tube.

https://www.youtube.com/watch?v=zb7WHaL_dz8

They vary in design but most of them are similar. You can get one from Walmart, harbor freight sears or just about any auto store and $20 will buy all you need.

When you get familiar with using it we will start diagnosing your problems.
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Old 09-20-2017, 07:00 PM   #6
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Re: ground issues and general wiring help

ace347, Vettevet has stepped up to the plate and you are in good hands. His commitment to help and wiring knowledge with pics is the best. Learn and enjoy, good luck
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Old 11-15-2020, 05:02 PM   #7
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Re: ground issues and general wiring help

Quote:
Originally Posted by notsolo View Post
you have probably done this, start under cab, clean frame and ground strap area on cab new star washers might help, move on to front end and frame, motor to battery etc. Good luck.....welcome aboard also.
damn nice work!!!
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Old 11-15-2020, 07:55 PM   #8
Andy4639
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Thumbs up Re: ground issues and general wiring help

VetteVet, is the man when it comes to electrical.

Just some general things to look at first.
Battery of truck grounded to frame are motor.
Motor grounded to frame.
Cab grounded to motor
Cab grounded to frame both sides
frame to bed both sides.

All light housing's are grounded to the metal of the truck some how. Clean all spots good.
Dash cluster should have a ground wire running to the dash also seperate from the harness.
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Old 11-15-2020, 10:53 PM   #9
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Re: ground issues and general wiring help

-
Old thread and the OP hasn't been on since 5/16/20. Don't know why it never went any farther. It ended kind of abruptly.....

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Old 11-21-2020, 03:02 AM   #10
ace347
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Re: ground issues and general wiring help

Sorry for not coming back, but I did figure it out, the hard way.

Apparently I wired all my turn signals wrong. The wireing instructions were not very clear from LMS. They claimed that if you had this one year, you use this wire and not that wire and so forth.

I eventually just made some jumper wires for the weather packs then trial and errored it till they worked. I can't remember the specific wire colors that I ended up with at the moment though.
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Old 11-21-2020, 03:40 AM   #11
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Re: ground issues and general wiring help

I learned this from a old low voltage electrician. Everywhere you have a ground , always use a external star washer between the wire and the item that you are grounding to. that will end your grounding issues.
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Old 11-21-2020, 08:35 AM   #12
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Re: ground issues and general wiring help

The frames on the 67 thru 72 trucks are riveted together. Not welded like newer ones. Over time (50+ years) those riveted joints rust (Resistance). This method worked fine when the truck was new. Running ground wires down to the frame will not always fix the problem. To use the frame as a ground you would need to run a ground wire from the left hand frame rail over to the right hand frame rail. Then you need ground wires from the radiator support to the frame, fenders to frame, cab to frame, box to frame and in your case, remote gas tank to the frame.
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