Ok mounting this lamp and I want to stay with it because it matches the car and because I already drilled mounting holes. I know dumb move.
Using a tail light bulb, two prong, fits in that perfect. The problem is when I flip the switch I can hear/feel the prongs move so that they pop off the contacts on the bulb and then I can't move the lever back. I will use an ohm meter tomorrow to find out if it's on the off or the other way around.
So there a bulb that is flush on the bottom so that it will rotate freely?
I think you can sand off most of the contacts on the bottom of the bulb without destroying it - but consider it as an experiment
A little dab of grease may also help?
Dielectric silicone based grease is used around high voltage, but at 6V ordinary grease should work, I think?
I think that you would find that a single filament globe with single contact is the only appropriate way to make this work.
Some designs had a floating keyed insulated disk that separated the rotor from the bulb. It just had two copper rivets in it. The rotor made contact on one side and the bulb made contact with the rivets on the other side. The rotor didn't contact the bulb directly.
I used to re-plate a lot of those dash lights and have seen a number of different designs. Even had to make switch stems, insulators and basically restore them before nickel plating. That's one of the reasons I don't do it any more. It wasn't hard to spend two hours making the switch work before getting to the actual plating task. And all for a few bucks for the plating.