OK here is my dilema. the interior lights on my 1964 f85 convertible stay on all the time. The car has been totally apart (frame off) I am getting it ready to take to the interior shop next week.

I put bulbs in the 4 spots (2 under dash, 2 rear) They all light! Shut doors they stay on. I then held both door switches by hand ( with help) I'm not plastic man. Still the same thing.

I made sure the headlight switch was not twisted to the ON interior lights.

I am assuming I have a bad ground somewhere.. Where is this circuit grounded? Any other suggestions?

 

It is grounded at the door switches and the headlight switch, if they are turned on, otherwise it is not.

In your case, it could be grounded at any of the switches, or anywhere else.
The switches are more likely, but really, it could be a pinched or skinned white wire anywhere (orange is hot).

- Eric

 

So is there a way to systematically figure out which switch is bad? If it is the switch.

 

I'd start by pulling the jamb switches out of the door jambs and isolating them. From there unplug the headlight switch. If that doesn't find the problem you'll have to start tracing wire looking for a bare or pinched spot.

 

I just finished installing the courtesy light harness in my 72 and experienced the same thing where the courtesy lights wouldn't go out. The problem was the white wire for the door switches had come out of the connector where the extra harness plugs in. After shoving that wire back into the connector, problem solved. Hope this helps to solve your problem!