Dome & pillar light operation?

[AR67GTX]

All my interior lights are on whenever my battery is connected. As I understand the circuit:

- power comes off the dome/stop/taillight fuse by pink wire through a piggyback connection at the brake switch that runs to the light switch.

- power from the light switch - piggybacked to power feeding the switch from the brake switch/fuse box - runs by a pink wire to each of the 4 lights.

- each light has a return yellow wire routed through the push switches at the door jamb which ground the circuits to light when either door is opened.

- The yellow circuits are tied back to the light switch which can also turn on the lights by completing the circuit by rotating light switch to turn on the interior lights (normally an open circuit).

Taking the door push switches completely out (no possible ground) still leaves the lights on. That leaves me thinking the light switch itself must be continuously energizing the interior light circuit and must not be breaking the circuit when the knob is rotated to turn them off.

I’m not sure of an easy way to trouble shoot the light switch. Pull it out of dash and leave the wiring connected and see if a trouble light shows a completed circuit between the pink and yellow wires when the lights should be off? Does the switch ground through the dash - I’m thinking it doesn’t.

I may also have a spare switch I can substitute and see if it solves the problem.

Anything else less obvious I may be missing here?

 

[toolmanmike]

Dome light switch in the door is where I would start. You probably have one with a broken spring. 50+ year old parts you know.

 

[AR67GTX]

They seem to be OK but will double check - I completely unscrewed them from the jambs so they could not ground at all and lights stay on.

just thinking that since a piggyback pink wire feeds both the lights switch and on to the individual interior lights, I guess completely unplugging the light switch should still leave the door switch circuits operational and if they shut the lights off then, that should point to a bad light switch?

 

[toolmanmike]

They seem to be OK but will double check - I completely unscrewed them from the jambs so they could not ground at all and lights stay on.

just thinking that since a piggyback pink wire feeds both the lights switch and on to the individual interior lights, I guess completely unplugging the light switch should still leave the door switch circuits operational and if they shut the lights off that should point to a bad light switch?

You do have the dash/dome light shut off on the headlight switch?

 

[AR67GTX]

Yes. Turning it causes no change in the interior lights staying on. It does still adjust the instrument lighting brightness when the headlights are turned on.

 

[toolmanmike]

Yes. Turning it causes no change in the interior lights staying on. It does still adjust the instrument lighting brightness when the headlights are turned on.

The dome lights operate through the door switches which provides a ground path. If the switch isn't bad it appears you are grounding somewhere in that ground circuit. A service manual/ wiring harness schematic will be your friend.

 

[dadsbee]

Just pull the wire off each jam switch.. no need to remove them.

 

[Jerry Hall]

The last headlight switch I bought was less than $15 at a O'Reilly's. @dadsbee has the best suggestion IMO. A pinched or scraped wire is easy to have on those long runs too.

 

[gtx6970]

Head light switch doesnt provide power to the lights. ,,,,,the fuse box does.

The switch provides ground to the circuit be it the head light or door jam switches .

When you roll the dimmer side of the switch all the way to the right , it provides a ground path for the circuit

 

[BeepBeepRR]

Use an ohm meter and see if it rings through on both terminals of the door switch. If it does then its stuck closed. If you push the button and it stops reading through the switch then the door switch is good. Move on to the headlight switch.

 

[AR67GTX]

Yeah, it’s all new dash and forward M&H harness except for the accessory harnesses I had to inspect and transfer over to the fuse box and new harness connections. I have the console back out and all the harness as exposed as possible and no issues found with it - double checked all colors, plug positions of conductors, etc against FSM diagrams and ClassicCarWiring schematic I also have for the 66.

Going to unplug everything off the light switch and put the jamb switches back and see what happens.

 

[AR67GTX]

Guess I didn’t hit post on that last one before heading to the garage.

fixed it. Pulled the plug on headlight switch but lights still stayed on. Disconnected harness plug to rear pillar lights and console lights started operating from door switches. The rear pillar light harness was unplugged when I bought the car so now I see why. Wondered if wires might be reversed in plug although I don’t see what difference it would make. Accidentally crossed a couple jumper leads creating a short and blowing the fuse. Replaced the fuse, plugged everything back together and voila - it all works right. Works from the headlight switch and from the door switches.

Not the first time I’ve done this. Once brought the temp gage in my old Corvette back to life by shorting it while bench testing it with jumpers on a battery. Still works good years later. - sort of like a defibulator resuscitation I guess.