How to test a switch

I would not rely on an ohmeter to test either switches or rectifier (alternator) diodes or any other high power device. The thing can make contact enough to "read good" but when put under load, may heat up and give trouble. It is way way better to test under a load. "an old headlight" or something else that draws a fair amount of current is better. I would say at least 5 amps depending on what the switch is made to do.

Hook it up in a circuit with your load device, and measure the voltage across the switch contacts. It should be very low, perhaps a few tenths of one volt. The higher the reading, the "worser."

I would say most any switch, heater, headlight, etc, that reads more than .3--.4V at the most is "trouble."

"Work" the switch on/ off several times, measuring when "on" each time.