How do you test the rearview mirror switch?

[JamesLond]

I saw a video on how to do it, but there's more wires on my Yukon's switch than what the guy has.

I think from the wiring picture, I should put a test light between:

B & F to test left mirror horizontal
B & C to test left mirror vertical

B & J to test right mirror horizontal
B & K to test right mirror vertical

I'm referring to the letters at connections around the power mirror switch box.

 

[Doubeleive]

I saw a video on how to do it, but there's more wires on my Yukon's switch than what the guy has.

exactly the same way he did, doesn't matter if it has more wires or not.
presuming you are using a incandescent tester light like does, polarity doesn't matter
just determine which wire is power and then test all other wires while pressing the button, no light=not working
keep in mind the mirror only moves 4 directions, power fold is a separate function in that case it only moves 2 directions.