JCM 2000 TSL 100 Momentary Switch Button...

[g1]

Momentary switches can be "normally open" or "normally closed". 3 pin types may do both at the same time, the center pin would be common, one outside leg would be the N/C side, the other outside leg would be the N/O.
The replacement switch you got just had the 2 sides reversed, it was probably a different brand or model number.
Glad you were able to flip the actuator and get it working.

[Enzo]

In fact, on most switches there should be a little NO and NC printed or embossed on the switch body. And C or COM for the common pin.

[DrGonz78]

Now I know what to call these parts and what to look for in the future. Thanks for all the great information!

[MikeH]

In fact, on most switches there should be a little NO and NC printed or embossed on the switch body. And C or COM for the common pin.

Whenever I get any of these switches in, the first thing I do is label which side in normally open and which side is normally closed with a silver sharpie. Most of the cheapies don't come pre-labeled.