1980ish K10 3 lights then 1 light on press

[jbchevyfan]

Really need some help with this. Chevy k10 79, 80, 81ish. Dimmer switch in one position, passenger side headlights (stacked) both work along with lower driver side. Press dimmer switch again, only top driver side works, as well, no taillights??? Taillights worked earlier. Dimmer switch was replaced also the actual light switch but everything was and still is wonky. Amy suggestions?

 

[PrairieDrifter]

Grounds. Check and clean them all.

 

[jbchevyfan]

So even though each light works when the dimmer switch is in different positions, it could still be the grounds?

 

[PrairieDrifter]

So even though each light works when the dimmer switch is in different positions, it could still be the grounds?

Yes. Are they all equal brightness?

 

[jbchevyfan]

Re: Brightness. Not really but the headlights aren't the same age and brand. This is a work truck my son and I have saved from the crusher as a learning project for both of us. We have it running great but the lights are the current issue and electrical is even further over my head than mechanics. So please forgive my ignorance but does each light have a ground that goes to the frame etc or is there typically one ground that all lights go to with only one connection to the e.g., frame? By the way, thank you for your helpful and super fast replies.

 

[PrairieDrifter]

The headlights should have a ground on each side of the core support near the top on the inside. Above the headlights. Per side not per light. Pass side should have a lead to the negative on the battery as well.

There's one from battery to frame, one from passenger rear of the head to the firewall.

There's one inside the cab above the parking brake lever, and there should be one tailight ground behind the tail light, I can't remember what year, but somewhere around 80 or so they put another tail light ground, so one behind both tail lights.

 

[Turbo4whl]

Could be two bad bulbs. Upper lights have two filaments, high and low beams. Lower headlights are only high beams.

So driver's side has a burnt low beam filament. Passenger's side needs Upper bulb too, burnt low beam. Or the connection at the bulbs are bad. Clean and check bulb connections first.

 

[kkgp81]

Grounds and possibly a wrong bulb. If you haven't replaced a bulb then for sure check the grounding. If your ground attachment on the firewall is on the parking brake pull the bolt and clean up the connections

 

[shovelbill80]

Are these sealed beams or buckets with replaceable bulbs? I'd check the connector on each lamp for corrosion, melting, etc. Backprobe each filament and ground for each lamp to check for voltage drop. How much voltage is at the battery when the truck is running? Do you have tail lights when only the parking lights are engaged at the switch?

Why not start with 4 brand new bulbs? Why not upgrade the whole kit-n-kaboodle with new lights and a relay harness? Headlights are probably the most important safety item behind good tires, and you'll be shocked by the light output with a quality high-performance halogen setup... Please don't even consider those garbage LED module things masquerading as bulbs.

 

[jbchevyfan]

Quick update. Drivers side top headlight connector was melted. Ordered new ones but for now removed the wires from the old connector, attached them to the headlight and now that one works. All four work but the passenger top was off once with only the lows. Reached behind the battery and shook the wires and it came on. Guessing a short it one of the three wires. Still no taillights but I will likely try to figure out how to run a ground from each taillight direct to the frame and see if that helps. Just not sure how to connect it to the taillight housing/connector. Thanks for all the posts. This old truck is my way to relax after work and it has been great learning more about these awesome trucks!

 

[Ricko1966]

Clean the tail light sockets they corrosion between the bulb and socket. Check the taillight fuse.

 

[Grit dog]

Tail lights have body grounds. Clean those up as well as the sockets.
And when in doubt hook up a temp ground. Like if you’re not certain of the condition of the bed to frame ground strap, make a temporary ground.

 

[75gmck25]

On my ‘75 the rear harness ground is a white wire (I think it is for both sides) that’s grounded to the frame behind the license plate area. I don’t recall if each tail light has its own ground wire behind the housing.

Also make sure the rear bulb sockets are clean and the two-pin tail light bulbs are correctly inserted. The socket is supposed to use a pin on the side of the bulb end to index it properly, but on an old socket somebody may have forced it and mangled the socket.

The rear harness also has a plug (1.5” diameter?) in the same area up behind the bumper. I bought a 4-wire trailer lights adapter and it just plugged in as a T in the wiring. If you pop that plug apart so that you have the half coming from the front wiring, you will have access to all the tail light wires and you can put a multimeter lead into the socket to verify/check voltage.

This is the Tekonsha 118311 T-connector I’m talking about. https://www.tekonsha.com/products/electrical-wiring/t-one-connector

 

[shovelbill80]

Quick update. Drivers side top headlight connector was melted. Ordered new ones but for now removed the wires from the old connector, attached them to the headlight and now that one works. All four work but the passenger top was off once with only the lows. Reached behind the battery and shook the wires and it came on. Guessing a short it one of the three wires. Still no taillights but I will likely try to figure out how to run a ground from each taillight direct to the frame and see if that helps. Just not sure how to connect it to the taillight housing/connector. Thanks for all the posts. This old truck is my way to relax after work and it has been great learning more about these awesome trucks!

Good start...

Serious question...Do you know how the factory lighting systems actually work...the long(resistance-riddled) path the juice takes from the battery/alternator to the bulbs in these decades-old vehicles? Newer vehicles, too.
As you've seen, it can be hazardous and possibly dangerous. Was the old 2-lamp system just modified with Scotchlocks and crimp connectors for the 4-lamp setup? Are you planning to really fix it or patch it up after you figure out the issue(s)? We can help you fix it once and for all...and it can be done in stages if loot is tight.

One of the best lighting setups I ever had was on this '86.
One of the first things I've always done on every truck I've owned was upgrade the circuits and lighting.

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[jbchevyfan]

So as it turns out, don’t use AI for a wiring diagram. I was checking the wrong fuse. Found the correct taillight fuse and it was and still keeps blowing when I turn on the lights. Obviously I am not an electrical guy so what might cause the fuse to keep blowing immediately after replacing the fuse and turning on the headlights?