Who has Dr. Diff 8 3/4 rear discs? Pt. 2

So I checked the pad pin in relation to the caliper piston and everything looks correct. I also placed a small piece of wood in between the piston and the caliper (with the caliper off) and pumped the pedal a few times and the piston moved just fine, so I know its working like it should.

I know the factory drum brake distribution valve is just a switch, but how do I test that to make sure its not closed? Take my meter and put it on the screw where the wire goes and then to ground?