Dome lamp don't turn off

[GMDad]

The dome lamp and under dash lamps are staying on and killing the battery..
I pulled both doorjamb switches but the wiring terminals won't fit thru the threaded hole for the switch so I can't check the wires... headlamp switch is other option. Is there an easier way to check this out ?

[kwmech]

Bare white wire to ground somewhere or a bad Headlamp Switch. How about the wire going along the sill plate.

[TKCR]

I would venture to say, it is the door switches. They probably need replaced, if they never have been. It is a pain to do. My wiring was laying loose between the panels, behind the kickpanels. They had rusted and broke off at the terminals. I just happened to find them when I was redoing the dash. I pull them out from behind kick panels and wondered what they were supposed to go to. After figuring out that they were the door switch wires, I took the door switches out and saw that the were rusted on the backside where the terminals once were.

Got new switches and I fished for my wires thru the door switch hole. And here's the hard part, especially on the left side, you can only pull 1 terminal out through the hole, at a time. If I remember right, the passenger side only has 1 wire.

[GMDad]

I played around for about 5 mins but managed to get the switch with wires thru the hole on the drivers side.
Had a new single contact switch I put in passenger side.. nope
took double switch from passenger side and put on drivers side...nope
changed headlamp switch...nope
pulled up sill plates and wiring looks good all along there...
Cant think of anywhere else unless I order a couple new switches an try them ??

[blindbug]

Originally Posted by GMDad

I played around for about 5 mins but managed to get the switch with wires thru the hole on the drivers side.
Had a new single contact switch I put in passenger side.. nope
took double switch from passenger side and put on drivers side...nope
changed headlamp switch...nope
pulled up sill plates and wiring looks good all along there...
Cant think of anywhere else unless I order a couple new switches an try them ??

There's probably a ground short somewhere in the wire between the door switch and the dome light. Can you take a 12v test light and connect one side of the light directly to the battery via long wire, and then connect the other side of the test light to the wire that comes from your door switch. If the light lights up, then you have a ground somewhere between the door switch and your dome light.

If you want to rule out the headlight switch, then connect the other side of the 12v test light to the terminal that connects your door switch to the headlight switch. There's diagrams around this website which detail which particular port on the terminal corresponds to where.

[GMDad]

I didn't think the door switch was hooked to the headlamp switch? Doesn't the door switch just supply the ground and as you were saying could be a short between door switch and lamp. The courtesy lamp also stays on.

[mongocanfly]

yeah...all the door switch does is makes the ground side of the light circuirt...its either the switch or a bare ground wire somewhere..if you had the door switch out and not touching metal and the lights still on,,then its somewhere else...most probably wiring..but the headlight switch does the same thing when you turn it to turn on interior lights..

[95 S_Trucker]

If you spin the headlight switch clockwise until it clicks, the dome lights will come on, even when the doors are shut.

Make sure the switch wasn't turned.

[TKCR]

Originally Posted by 95 S_Trucker

If you spin the headlight switch clockwise until it clicks, the dome lights will come on, even when the doors are shut.

Make sure the switch wasn't turned.

I thought of that too later, but you already suggested that

[GMDad]

I rotated the knob clockwise and when it clicked the dome lamp got marginally brighter
I borrowed a continuity meter to check each of the individual wires to see if there is a break in any of them. Tomorrow's job.

[mongocanfly]

you can use that meter to check and see if your ground wires grounded as well...

[stanski]

Just a WAG, but could either the dome or courtesy light be continuously grounded through the light housing mounting? If you unscrew both of those and let them hang the lights should work properly. If you touch either to ground and they stay on, that could be the problem? Had same issue when I installed underdash light on my 58 then realized the housing could not be screwed directly to metal it needed a plastic insulator.

[blindbug]

The fact that when turning your knob clockwise and when it clicked the dome lamp got marginally brighter should be a tell that the headlight knob isn't the issue. If the dome light is getting brighter, then that should mean that when it clicks, it's getting a proper ground and thus causing the light to be brighter.

If you have a multimeter, check continuity between the wire that's attaching to your dome light, at the dome light, to a ground location. It's got to be the wire getting a ground when it shouldn't be.

[GMDad]

Another perplexing morning. I checked the white wire from passenger switch to courtesy lamp in middle of dash...no breaks
Checked from lamp to drivers switch and no breaks
Checked from drivers switch to the dome lamp bulb connector...no breaks. I have taken the dome lamp housing out as when this started I didn't see the light has stayed on during the day but got hot enough to melt housing (and it was a LED bulb) so now just have orange and a white wire hanging from headliner. So I unscrewed both sides switches and left the wires connected and let the switches hang free in the air. Courtesy lamp still on. Only thing left was to pull the headlight switch out and still courtesy lamp is on... the tail lamp and courtesy lamp are on the same fuse. Could I have a problem in tail light area ?
I am a novice at chasing wiring so buddy coming over after lunch. Says he'll have it fixed in 5 mins... hope he's correct as I am running out of ideas

Another quick question... the courtesy lamp has 3 white wires running from it. One to drivers switch, one to passenger switch but can't figure out where the 3rd one goes. It could be my problem as it is joined in the same terminal as drivers switch white wire ?

[hatzie]

What year is your truck?
It makes a difference in how the ground is sourced through the dome/courtesy circuit.

The door jamb switches ground through the switch to the sheet metal where they pierce the body. The switch closes the circuit between the wire terminal and the switch body when the door opens.

The headlamp switch grounds to the dash frame. This ground is closed to the dome wiring when the plunger is rotated until it clicks.

On some years there's an additional tan ground wire between the ignition switch and the LH door jamb switch making two connections on the LH switch.

There really aren't that many ground wires. Isolate them at both ends and then test continuity to a chassis ground.
Pulling the jamb switches out of the jamb and the headlamp switch out of the dash, or just unplugging it, where they can't touch metal should effectively isolate them.

If you stop getting continuity re-install each switch and re-test. Obviously, the doors MUST be closed or the jamb switches will make contact.

If you're still getting continuity to ground unplug the courtesy lamp and re-check. If your ground goes away carefully use plastic isolation washers to mount the courtesy lamp.

[GMDad]

It is a 1986 C10. Funny thing it had plastic washers under the head of the door switches on both sides. Both sides were double contact and had a rubber sleeve on the plunger end so I am presuming factory switches.
The courtesy lamp is a plastic housing with a single screw mounting it.

I have printed off your schematics for the cab wiring and the white wire from courtesy lamp shows going to "156" but I haven't been able to figure out what that is... thanks

[hatzie]

156 is the circuit number so you can follow the circuit 156 wires through the diagrams... across splits in pages and past tangles of other wires on the diagram etc. GM took it to an extreme in 1987 eliminating the single wires you can trace making it very difficult to read the 1987 wiring diagrams.

The reason to show the circuit number in plug cavities is to show the position of that wire in that connector.

[GMDad]

And my drivers switch does have a tan and a white wire on it so the white goes to the dome lamp?

[Pontiac1976]

Just thought you might check the rear dome light wiring to the left seat post some time the wire short there. It should un plug @ the post and run up the roof to the dome.
should be onrange wire and white wire.

[Palf70Step]

Unplug the dome light harness from under the dash. See if trouble goes away. This will help you to isolate which section the ground is coming from.

[GMDad]

After more than 4 hours pulling the truck apart and tracing wires the problem is the cargo lamp socket where the wires connect. The cargo lamp harness goes along the inner roof and down the back post and in behind the drivers side rear speaker is a connector that goes from the orange and white wires from door jamb switch and fuse block and is connected to 2 double terminals. A larger white (ground for cargo) and a smaller white (ground for dome lamp) on one terminal and the second terminal has the larger orange (power for cargo) and a smaller orange (power for dome lamp). Ground back fed from cargo lamp socket thus putting the dome lamp on. Now to put it all back together but not today.
Has anybody ordered the cargo lamp harness from LMC. Its $29.95 just curious if socket is on it. Looks like it in the catalog

[mongocanfly]

when I redid my truck I wired my cargo light separate from my interior light...I didn't like having my interiors on for the cargo to work..just a idea

[TKCR]

I know I replaced my harness, it was a pain in the a$$ too. I believe the socket was on there, if I remember correctly. I replaced the cargo lamp and dome light housing, at the same time. Put led bulbs in them, so they don't get so hot when they are on.
It would be a good time to add more light under the dash since you been tearing into all the wiring. I added this kit from LMC. http://www.lmctruck.com/icatalog/cc/full.aspx?Page=204
It added 2 more lights to the one under the dash and added LED's in it too.

[akart]

I had that problem w/some other EL issues too. It was a fuse.
So, might want to check that.

[TKCR]

Originally Posted by akart

I had that problem w/some other EL issues too. It was a fuse.
So, might want to check that.

He found the issue, it was a bad socket in the cargo lamp