1979 K20 Headlight Open Circuit

[rileysbc400]

I have been building a 79 K20. The truck was purchased as a incomplete project, so there’s a lot of things up In the air about it. I’m new to wiring and electrical, but know most of the basics. I installed this fuse panel with the rest of the harness. Everything works as should, except the headlights. I’m not sure if I’m missing a place for a fuse or what, but no headlights what so ever, and no blinkers. There’s a spot on top of the fuse block that I wasn’t sure was for, it’s a white plastic clip. Was wondering what the white plastic clip was, and what might be keeping my headlights an open circuit?

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[Big Chip]

Here's the wiring diagrams:

https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

 

[AuroraGirl]

note, not all my fuses/cans are inserted. But this is an 1980 GMC k25 fuse panel, it should be the same one. Those orange wire taps are important generally speaking , not sure if to the headlights, but you probably need a few things yet plugged in.

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The lower left corner, N, it says "LPS" and the diagram isnt really helpful but LPS means to me, lamps, and that feeds something. no idea what tho.

 

[Matt69olds]

Lamps is the fuse for the dash backlighting.

The white plastic plug on top of the fuse box is for the seatbelt warning buzzer. It might also be for headlight warning and key buzzer.

I recall reading about someone else having similar problems as you are, thru found out there were some wiring changes made to the various years of fuse box/ forward lamp harness. You may need to move some wires around in the headlights harness it would help if you knew exactly what years all the different parts are from.

 

[Rickf]

Should there be two flasher relays? One for the blinkers and the second for emergency flashers. When I had dead headlights on my old '84 it turned out to be a bad fusible link near the starter.

Does the '79 have a floor mounted high/low beam switch or column switch?

 

[AuroraGirl]

Should there be two flasher relays? One for the blinkers and the second for emergency flashers. When I had dead headlights on my old '84 it turned out to be a bad fusible link near the starter.

Does the '79 have a floor mounted high/low beam switch or column switch?

Floor mounted switch and yes two flashers. My trucks fuse box was missing one of the cans because I stole it for another application, and the random missing fuses was me depowering things not actually needed since the god damn wiring is... I would just rather not power a circuit i dont know where the wire goes lol!
IF OP needs to see a forward lamp harness I have a 78-79 (not sure which) harness sitting in my shed in good shape too

 

[Rickf]

I should have been more specific. I was refering to Riley's image of a fuse panel, the spot for the second flasher (missing?) is out of the frame. I also noted that there appears to be wrong amperage fuses in some of the spots. Lack of headlights could also be a faulty floor switch.

 

[Big Chip]

I should have been more specific. I was refering to Riley's image of a fuse panel, the spot for the second flasher (missing?) is out of the frame. I also noted that there appears to be wrong amperage fuses in some of the spots. Lack of headlights could also be a faulty floor switch.

I second the floor switch.

 

[rileysbc400]

I took a test light to the back of the fuse block , without the harness attached. It seems like I’m getting power in the fuse box where I should. The terminal of power changes when high/low is activated like should with the floor switch. Might be an issue with the headlight harness itself. I have checked all of my grounds. I got two of the bottom lights working. No blinker, horn, hazards, or main headlights though. I do have that second flasher installed by the way. Appreciate the reply’s, and the image of the fuse block. It will definitely come in handy. I’m going to try to get the right fuses where I need them.

 

[AuroraGirl]

I took a test light to the back of the fuse block , without the harness attached. It seems like I’m getting power in the fuse box where I should. The terminal of power changes when high/low is activated like should with the floor switch. Might be an issue with the headlight harness itself. I have checked all of my grounds. I got two of the bottom lights working. No blinker, horn, hazards, or main headlights though. I do have that second flasher installed by the way. Appreciate the reply’s, and the image of the fuse block. It will definitely come in handy. I’m going to try to get the right fuses where I need them.

do you have a ground connection from cab to fender, fender to battery, battery to frame, battery to engine? 2 from engine to cab is wise too

how about the bus bar in the cab?