My mechanic friend Vince Sauberlich comes to my garage on Thursday nights to tinker with the cars. Last night there wasn't all that much to do, so I dragged out a headlight switch for my '53 Pontiac that I must have bought at a swap meet a long time ago. I bought it from Jerry Longrie of Minnesota and it still had a $10 sticker on it.
The switch on my car worked the headlights fine, but the dash lights were another matter. They would only work when I twisted the knob to exactly the right spot. Sometimes it took a half hour to "dial-in" those dash lights, which is no fun on a dark night.
Even the contacts on the NOS switch had green stuff on them from sitting around. So we sprayed them with electrical contact cleaner and cleaned them with my trusty Dremel tool. When we put the new switch on the car, the dash lights worked fine on the highest setting, even though the rheostat action didn't work. This was still a big improvement over before.
Since we still had time, we decided to play with another headlight switch for a '57 Buick. Eventually we found a removable panel that gave us just enough access and we got the old switch out. The "new" one in this case was from a junkyard car and we decided to take it all apart and clean the pieces. There are all sorts of springs and little pieces inside that will go flying across the room if you're not careful. Vince is very careful. After we cleaned and re-assembled the switch, we found it worked the same way as the Pontiac switch - no rheostat action, but the dash lights came on bright every time.
Apparently the contacts for the rheostat (a kind of coil spring embedded in ceramic) tend to fail with age. Luckily, the old switches can still be cleaned up and made to work on an on-off basis, which is pretty good when you consider both cars are more than 50 years old. Do you think computer-controlled dimmer mechanisms will last as long? I doubt it.