74 c10 Dome Light issue

[crazymax]

Anyone have a clue about this one. Vehicle is a 1974 chevy c10 step side - Just out of the blue (no apparent reason) the dome and courtesy Light started working in reverse (door open Lights off – door closed – lights on) . I have checked the door switches and both are functioning properly. I have removed the door switches and the headlamp switch and still the lights stay on. Anyone have some suggestions?:


waah:

[MountainGoat1966]

I am putting my brain back in gear to try and come up with some ideas.

My first and usual response to anything this weird would normally be it's the same space aliens that mess with me here.

I'll post any ideas I come up with.

Meanwhile, keep your chin up.

[MountainGoat1966]

Here's a thought:
Did you check under the door sill trim to make sure there isn't any bare wire shorting to ground when it shouldn't ?
Door closed can apply pressure to the door sill. Open might allow movement and let the wires move also.
Just a thought worth checking out.

[tucsonjwt]

My only experience with this is that the switches in the door pillars are tricky. If you just turn the nut to remove them the entire switch turns, and you end up twisting and/or shorting out the wires connected to the switches.

You have to hold the center plunger somehow when you remove them, then gently pull out the switch as far as you can. Likely, you will see a lot of twist on the wires somewhere and possibly some bare wire - at least that was my problem.

I remember seeing a post somewhere on this site about the switch being in a normally ungrounded condition when the door is closed, and the ground being engaged when the door is open.

Currently, my switches sometimes do not work because the door weatherstrip is too big and rubs against the plunger, preventing it from completely releasing when the door is open. Maybe you have some similar interference with the plunger operation.

[crazymax]

Thank you for your response Tucsonjwt checked and problem still exists

[tucsonjwt]

When all else fails, time to read the instructions. Can anyone post the wiring diagram? I think I have one in an old chilton manual but it I can't scan it.

As I recall, this is a very simple circuit, so it should be easy to trace.

I would think if you have the switches functioning exactly in reverse, then you have the polarity reversed somewhere. I suppose this could even be internal in one of the switches. You have new switches?

[crazymax]

Thanks MountainGoat,

The Lights stay on when the doors are open with the switches removed - This one is a head

scratcher.

[crazymax]

Tussonjwt
Thanks for your offer for the schematic - I do have the factroy gm manual and the wiring supplement manual. I was hoping someone had encountered this problem in the past.

Obviously I am getting some bleed from another circuit if the lights are coming on when the door switch is ungrounded. I have spent hours going over the schematics to see where this circuit may cross paths with another.

Would welcome any suggestiions

Thanks

[tucsonjwt]

So, you have ruled out that one of the switches could be defective internally (i.e. shorting out internally) and causing the problem? New replacement switches are available as aftermarket, I think for about $4 each.

The wires to/from the switch to the lights and power source are not stripped/rubbing against another wire or connector? I would start at the fuse box. Worst case, run new wire and switches from scratch from the dome light circuit. This requires fishing new wires through the kick panel and floor/door pillar, but you are there now anyway.

In my truck, previous owners have hacked the wiring for various mods so much that I have wires and connectors hanging down under the dash everywhere. I have had the operation of the brake and clutch wear on wires and cause electrical problems.

[crazymax]

Sorry tucsonjwt,
Last day has been busy with domestic duties (honeydo list). Ok heres where it stands - ruled out switches, checked wire under door jam, removed and checked courtesy light, still have the problem - Did notice one thing though - the courtesy lamp functions normally now just the dome light goes off when door open comes on a lot dimmer than normal when the door is shut.

[Gordonr1973]

Check your wires coming out of the headlight switch too. It's grounding out somewhere I'd guess. Did you install anything just lately that you might have drove a screw through?

[crazymax]

Done - I want to thank everyone for their suggestions on where to look - It appears that the problem was the cigarette lighter receptacle was shorting to ground -

Again thanks to all!!!