Dome lamp ground short circuit questions.

[Grit dog]

and noted all the white wires join up above the E/brake assembly. Also there is a possibility of interaction between the mechanical movement of E/brake and the wiring in this area..

That’s good to know, thank you.
Not as much visibility under my dash without removing AC ducts. I hadn’t seen that.

 

[Grit dog]

Bringing this back up for the guy who had the courtesy lamp issue...

 

[Grit dog]

Back to the top for the dome light switch guy.

 

[shinkle]

I had an issue with my 87 blowing fuse on this same circuit. The dome, courtesy, cargo lamps are on the same circuit with the horn, radio, and cigeratte lighter. I did what poppy87 suggested but in reverse. Unplugged everything, put in a good fuse, plugged each one in at at time until the fuse blew. It was the cigarette lighter.

Look beyond the lamps and lamp switches. When the problem is occuring unplug or power off each one of the above until the light goes out. I'm betting cig lighter, they are notorious shorts.

 

[Big Blue Square]

Same problem on my 87 K5. Rheostat is definitely sketchy (are these available aftermarket?) but the weird thing is both dome and cargo were working fine until I pulled the 20A fuse to keep the lights off with door open during unrelated project. Put fuse back in...nada. Neither has voltage now in any switch position. Small courtesy light still works fine...it shares the circuit with the door grounds but a different fuse according to my trusty shop manual. What should I be testing? I don't even drive BiG Blue at night anyways but it bugs me.

 

[Big Blue Square]

Started unplugging things including remove headlight switch completely, black tape all the hanging down stereo wires, then at some point the domes come back on! No idea why...must have bumped something in the right way. Electrical issues....sheesh. When the wife sees me laying on the floorboard with the driver's seat pulled out she knows to walk away.

 

[Juan Cano]

Great thread and tons of great info. I am the new proud owner of an old 1986 c10 long bed. I am having a similar issue. My interior dome light didn't have a bulb so I put one on and it's on full brightness all the time, even with door closed. I replaced the housing and same issue. Then I checked the outside cargo light and also didn't have a bulb, replaced it, and same thing, on all the time. As a coincidence (or maybe not), the dash lights do not work at all Not sure if it's related as I haven't taken the dash out to check the lights but I imagine it would be super rare for all the dash lights to be out.

Questions: What is a courtesy light? And this cargo light, I hear about a switch. Is there a switch to turn it on? How is it supposed to work?

All other headlights, blinkers, parking and brake lights work fine.

 

[Juan Cano]

Great thread and tons of great info. I am the new proud owner of an old 1986 c10 long bed. I am having a similar issue. My interior dome light didn't have a bulb so I put one on and it's on full brightness all the time, even with door closed. I replaced the housing and same issue. Then I checked the outside cargo light and also didn't have a bulb, replaced it, and same thing, on all the time. As a coincidence (or maybe not), the dash lights do not work at all Not sure if it's related as I haven't taken the dash out to check the lights but I imagine it would be super rare for all the dash lights to be out.

Questions: What is a courtesy light? And this cargo light, I hear about a switch. Is there a switch to turn it on? How is it supposed to work?

All other headlights, blinkers, parking and brake lights work fine.

 

[AuroraGirl]

Great thread and tons of great info. I am the new proud owner of an old 1986 c10 long bed. I am having a similar issue. My interior dome light didn't have a bulb so I put one on and it's on full brightness all the time, even with door closed. I replaced the housing and same issue. Then I checked the outside cargo light and also didn't have a bulb, replaced it, and same thing, on all the time. As a coincidence (or maybe not), the dash lights do not work at all Not sure if it's related as I haven't taken the dash out to check the lights but I imagine it would be super rare for all the dash lights to be out.

Questions: What is a courtesy light? And this cargo light, I hear about a switch. Is there a switch to turn it on? How is it supposed to work?

All other headlights, blinkers, parking and brake lights work fine.

I do not remember where but the Cargo lamp is a black switch that is a small rectangle and has a slider. It allows the interior dome to be turned off all the time too I think? Courtesy lamp is the one floor lamp

your bad back lighting… grounds or fuse first check. See if your bulkhead has any melt or wires shorting to power on another circuit.

 

[Juan Cano]

I ordered a new AC Delco Headlight switch, because, why not?

 

[AuroraGirl]

I ordered a new AC Delco Headlight switch, because, why not?

It’s possible that could be at fault. I do believe the circuit can have more than one odd issue do the same thing so not a bad idea they aren’t exactly forever items. Not to mention, they carry the full current too not just a simple on off signal for a relay or an input request to a computer

 

[Juan Cano]

It’s possible that could be at fault. I do believe the circuit can have more than one odd issue do the same thing so not a bad idea they aren’t exactly forever items. Not to mention, they carry the full current too not just a simple on off signal for a relay or an input request to a computer

We’ll see. The replacement came today but the ceramic part was cracked and a tab broken. Sigh. Replacement should be here Friday. Not sure if I’ll be able to do this weekend, have a terrible neck pain.


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[Grit dog]

Sounds like headlight switch is a solid possibility. Also available at any parts store for cheap. Surprisingly in stock part.
headlight switch powers the cluster lights and is on a rheostat to adjust brightness. If turning the knob back n forth doesn’t make the cluster lights get brighter and dimmer, likely the rheostat. And full turn on the headlight knob turns on the dome light.

Take a good look at the wiring diagram I posted. The dome and courtesy lights are hot + all the time and either the headlight switch or door jamb switches connect to ground to turn them on. If they stay on constant then ground is made either at the switch, door switches or a short somewhere.
You can disconnect those 3 things 1 at a time and see if any of them make the dome lamp go out. Door jamb switches tend to short to ground. You’ll understand if you see one.
Also cheap and in stock in a lot of parts store and likely are old and crusty anyway.
Cargo lamp is always connected to ground when the dome light is on and the switch on the b pillar connects +.
Turn that switch off and cargo lamp should go out even if the other stuff is an issue.

caveat is this is if the wiring isn’t butchered up somewhere.
And to remove the pull knob to replace the headlight switch there’s a spring tab on the back side of the switch. Depress to pull knob out then whole switch unclips easy.
Probably take you 10 minutes to find that tab the first time and 10 seconds thereafter…

 

[Raider L]

@Grit dog,

I have a similar issue with my dome light, not working and have full power at the white and the orange wire. Anyway,the junction is, believe it or not, at the floor courtesy light! All white wire power/ground is going to and away from the floor light at the heater vent. At least on my schematic. There's like four white wires that come together there, one for each door jam, and one for the light there, and one going up to the dome light. Now, why did the engineers think that was okay? Check the connection there to see if there's a problem.

 

[Raider L]

@Grit dog,

I have a similar issue with my dome light, not working and have full power at the white and the orange wire. Anyway,the junction is, believe it or not, at the floor courtesy light! All white wire power/ground is going to and away from the floor light at the heater vent. At least on my schematic. There's like four white wires that come together there, one for each door jam, and one for the light there, and one going up to the dome light. Now, why did the engineers think that was okay? Check the connection there to see if there's a problem.