No headlights after adding ground strap

[379redneck]

Hey everyone. I’m trying to straighten out a few electrical problems on my drawn out frame off. I tried getting the truck to run yesterday and couldn’t get it to crank. After messing around for awhile I found that the entire truck was energized but things still worked like the headlights and gauges, but not the starter. I ruled it out to be be a ground problem as it went away and now cranks after I added the big ground strap that goes from the motor to the frame (the truck never had this before and it was never an issue). After adding the strap I lost my headlights. The turn signals work, but no headights. So with a bad ground the lights worked, then with the motor grounded properly they don’t. I had the ground wire from the rad support on the negative on the battery. It’s not the best connection but I would think I should get something out of the lights. Anyone have any thoughts?

[RustyPile]

Originally Posted by 379redneck

Hey everyone............….<snip>............So with a bad ground the lights worked, then with the motor grounded properly they don’t. I had the ground wire from the rad support on the negative on the battery. It’s not the best connection but I would think I should get something out of the lights. Anyone have any thoughts?

With 99.99% certainty, I can say adding that ground strap had nothing to do with loosing headlight function.. You won't fix the headlights by removing it. You said something like "after messing around", you added that strap.. Is it possible your "messing around" created the headlight problem? Fix that radiator support ground -- make it the best ground you can.. If the lights still don't work, treat the troubleshooting like it's a totally different problem.. Turn on the lights and check for voltage at the headlight bulbs.. Check the dimmer switch.. Check the individual bulb grounds on the core support.. Check the bulbs themselves.. I'm betting something got disturbed during your starter repairs..

[379redneck]

Yeah I definitely have to keep the new ground. I didn’t mess with anything for the headlight wiring. I was just checking some of the ignition wiring and things like that
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[RustyPile]

Originally Posted by 379redneck

Yeah I definitely have to keep the new ground. I didn’t mess with anything for the headlight wiring. I was just checking some of the ignition wiring and things like that

Assuming that's the case, starting with fixing the radiator support grounds, conduct the light circuit tests I suggested and post the results here.. If you don't understand or know how to do those tests, let us know and we'll walk you through..

[toolboxchev]

Yup, Rusty is very good at helping folks out. Got me through a complete wiring harness restoration.

Have a look at all the fuses. Even the ones in the lighting circuit up on the Radiator Support. What year truck are we working on?

[379redneck]

I’m not sure on the tests you mean, but I did find this. The fuses on the left side of the fuse box don’t have power in or out. I was also having an issue with my fuel pump not coming on but now that’s probably related to this. Truck is an 87 k20
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[RustyPile]

Originally Posted by 379redneck

I’m not sure on the tests you mean, but I did find this. The fuses on the left side of the fuse box don’t have power in or out. I was also having an issue with my fuel pump not coming on but now that’s probably related to this. Truck is an 87 k20
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It sounds like you have several problems going on.. You'll need a wiring diagram for your truck.. Diagrams are available for download in the ELECTRICAL FORUM.. Since you mentioned the headlights, let's tackle that first.. The headlight's circuit isn't protected by fuses.. The headlight switch has a built-in circuit breaker that serves that purpose.. There is a main power circuit (12 ga. red wire) that starts at the battery and travels through out the vehicle providing power for various circuits..

The following tests are lengthy and there are shortcuts to the process.. I'm giving you the "long version" so that you'll fully understand how the circuit works and the route taken by the wiring..

Go to the headlight switch and, using a dvm, check for voltage on that red power feed wire.. If no voltage is present, trace the wire back to it's junction with the main power feed, checking for voltage while looking for an open (break) in the wire.. If you have voltage at the headlight switch, turn on the headlight switch and check for voltage on the light blue wire.. If no voltage there, the headlight switch is bad.. If voltage is on the light blue wire, gain access to the dimmer switch and check for voltage on the light blue wire on it.. If no voltage on it there, you have an open on it somewhere between the dimmer switch and headlight switch.. If there is voltage on the light blue wire at the dimmer switch, check either of the 2 other wires.. Depending on whether Hi or low beams is selected, you should have voltage on 1 of them.. Depress and release the dimmer switch and voltage should appear on the other terminal.. If you don't have voltage on both (one at a time) the tan and light green wire, the dimmer switch is bad.. If the dimmer switch passes the test, check for voltage at both headlight bulb sockets.. No voltage?? Open wire(s) between the dimmer switch and bulb sockets.. Voltage present?? Bad bulbs or bad ground..