I've have a back up switch connected to my SM420 for a few years now. Have 2 separate female spade terminals connected which has never encountered very much if any, road grime. Think you'd be just fine with your plan of attack.

Craig

My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear
My truck ....... Respect The Rust
If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.