How do you check the multifunction switch??

Ok, non mechanic fumbling here. Here is where I sit.

checked bulbs, good but replaced
checked #11 15 amp fuse good but replaced
checked brake light switch good but replaced

the back is built out and I’m trying to troubleshoot without pulling the shelving. 😂

I’m on to the multi function switch now. I don’t know the color of the wire coming into it to see if I have power going in, and I don’t know what wire to check going out as I don’t have a diagram.

im tempted to just buy a multifunction switch at 150 bucks, but that ain’t like a 6 dollar bulb.

Can somebody tell me how to test the multifunction switch in place before I spend 150 to replace it?

 

My bet is on a bad wiring for the brake lights. Sockets and exterior wiring is where I would look first.Start from the rear and work your way up front. I doubt your multifunction switch is bad and don't see the relationship with the brake lights.Are your turn signals and park lights working in the rear?