MTFCA Forum

Photos of my starter switch. Is there a way to determine if the switch works before I try it in the restored car? Should I take it apart to see how the inside stuff looks?

You can do some basic tests with an ohmmeter. Neither of the terminals should show continuity to the body of the switch or to each other when the switch is not pressed. When the button is pushed down firmly, the meter should show 0 ohms between the two terminals and no continuity to the body of the switch. The switch button should move freely without scraping or binding. The terminal post nuts that hold the terminals to the switch body should be tight and the insulating washers located under the nuts should be in good condition. I don't know if parts are available to rebuild the switch. Insulating washers are probably available. These tests are not conclusive, but a switch that passes them will probably work. The only way to know the true condition of the working parts is to remove the rivits and take the switch apart and inspect the innards. It's a very simple device, but it must function well at very high current loads and it must be free of any tendency to stick. Dirt, rust, mechanical wear, weak spring, etc. inside the switch will make it unreliable. The contacts in these switches tend to erode and burn away with use. If quality repair parts are available, most of them can be rebuilt to work as new. A bad switch can lead to starter damage and/or battery damage, or even a fire.

Yes the original switches can still be good. This one has two screws that hold it together. Other have tabs that are bent over. Either way they can be taken apart and cleaned up.
Use a thin back up wrench to keep from turning the copper stud with the fiber washer.

Years of use can burn the copper strip contacts that’s in them. Some are really worn thin and others not so much. It’s those fiber insulating washers that you need to be careful with. Use WD-40 to lube the copper studs so you won’t have to force the nuts to turn off and keep from damaging the fiber washers.
Ace hardware has fiber washers you can fabricate for replacement insulating washers. You use to could find old switches at swap meets fairly often that can cleaned up and reused.
Good luck with yours.

Easiest and maybe best to connect it with some heavy jump leads to that rebuilt engine you have and try it.

Typically, the 2 studs get turned 180 degrees. Virgin contact area. If the button connector strip is still solid, clean it up. Dress/Polish contact areas.
Fiber washers must fit well. replace as necessary. Good as new.

Be sure the switch works well mechanically as well as electrically. It must work freely without binding and it must have a good spring action to raise the plunger when released to prevent it from sticking. You DO NOT want it to stick in the "on" position. When using the switch, step down on it squarely and firmly to engage the starter and hold it down firmly until you intend to release it. It's important that the switch plunger moves freely so as to make a quick, clean contact on engagement, and it must also move freely to allow a clean, quick release of the contacts. When releasing the switch, take your foot completely off of it.

The switch you have is the early version, and is easy to take apart. There you will see the condition of the contacts. If they are good, clean everything up and reuse.

I had gotten a frame and running gear which had sat outside for who knows how long. I took the starter switch off and soaked it in apple cider vinegar to de-rust it but it didn't work. I took it apart and the two contacts were dirty and worn. I smoothed them out and cleaned and repainted and lubricated it and it now works perfectly. The spring was strong and it's as good as new. Remember, the original parts are much better constructed than the current repros, so make the originals work if you can.
Here's a photo of the switch when I got it:
John