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FYI - I just fixed an issue on my Roadmaster where the DOWN button didn't work (on either mirror) but everything else worked. If you're having this problem, this should help you:

The Roadmaster power window switch is horizontal and easily collects water if you're not careful about keeping your windows up during rainshowers. The Caprice power window controller is mounted vertically and is much more weather-resistant (the wiring pinouts are completely different, BTW).

I took the controller apart and all switches tested good. Then I plugged it back in with enough room to backprobe the connector pins and started diagnosis. GM designed it such that all wires stay at ground until you push a button which then puts 12V on that wire, causing current to flow through the motor and move the mirror. The 12V feed for the Roadmaster mirror control is the center pin of each 3-pin switch.

As I probed the circuit board, I found no voltage on the center pin of the DOWN switch. I started following the trace and found a break in the trace. Once I made a jumper and soldered it in, everything worked again.

In the process of visually inspecting the circuit board, it appears that water had gotten in and started to delaminate the board in several places from the outside edges in . I made some other repairs to keep it healthy.

Moral of the story - if one action doesn't work for both mirrors, check for 12V on the center pin of the dead switch, then find the break in the trace.

And keep water off your mirror controller!
 
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