How to check a backup switch

That is not the correct switch. All 4 speeds have a 2 prong switch, and the ones I've seen are flat/ spade "push on" or "flag" terminals.

That there appears to be a combination neutral/ backup switch for a Torqueflite off a 68/ later car

Here

http://www.brewersperformance.com/proddetail.php?prod=BLS814