Another Electrical Hell Issue (Brake/Hazard/License lights '90 K1500)

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sirmacbain

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I'll document this fix as I work on it in case it helps someone else, OR hopefully someone has an answer/help.

I bought a 1990 K1500 and since day one it's had brake/hazard/turn/license light issues:

If I leave the brake fuse in (labeled "stop" in the box):
* the license plate lights stay on with the ignition turned off / keys out
* the turn signals don't cycle (they stay powered on)
* the hazard lights don't cycle, nor do they power the rear brake lights
* the brake lights don't light at all

If I remove the brake fuse (labeled "stop" in the box):
* the turn signals flash as expected
* the hazard lights don't cycle, BUT they DO power the brake lights

The headlights function regular/hi beam and the dash indicator works.
The backup light works intermittently (it cycles on off randomly).
The parking brake / brake indicator light is always on.

What I've tried:
I've replaced the brake relay, brake light switch, turn/hazard relay, replaced all bulbs.

What I haven't done:
* pull ABS codes from OBD1 (I believe the ABS error signal is on the same light as the parking brake indicator, maybe wrong)
* check grounds / voltages at various points on chassis harness (I bought new engine block ground straps, haven't put them in yet since the engine, radio, etc all run fine)
* replace parking brake switch
* replace hazard switch (on steering column)
* replace bulb sockets/receptacles - or clean them with contact cleaner
* replace the backup light switch (on transmission)

What I don't know:
* the fuse box has 2 30amp fuse/breaker slots labeled "power", it had nothing in them when I got the truck, consulting the Haynes/Chilton I think these are supposed to be breakers but not sure their function
* the fuse box has a "DRL" day time running light slot that looks like the connectors were pushed in / failed, with a missing fuse, BUT it may be that the truck simply doesn't have DRL, I need to figure out a way to check if the truck should have DRL

What concerns me is that for the license lights to stay powered with the ignition off makes me think something is shorted. So, I don't think it's just a bad ground, but I also likely have bad grounds / connectors.
 

sirmacbain

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Following the Chilton analysis for the brake warning light:
* tried pulling the ABS codes: nothing
* disconnected the "combination valve switch" on ABS: light still on

Next steps are disconnecting the parking brake switch to determine if it's bad. Also, replacing the engine grounds, cleaning contacts on the "stop" circuit and circuits with mixed grounds with it, trying to find a short in "stop" circuit - however, the Chilton manual doesn't have the best electrical diagram (tho it's better than the Haynes by far), so I'm ordering the "Detroit Iron" reprint of the official repair manual (2 volume 1400 page, hopefully it has full circuit diagrams). Right now, unless I cut open the wire harness and literally follow the "stop" circuit I don't have a way of seeing what it's all connected to.


The 2 unknown fuses slots appear to be 30amp "breakers" (not fuses) for accessories (CB/radio, power lock mods etc). It looks like it's normal for the box to have a DRL fuse slot without contacts - I'll verify that I don't have a DRL setup.

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evilunclegrimace

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