Once we used a digital multi-meter to confirm that the power supply was working, we removed the six screws and took the cover off to check the switch output. The switch was somehow defective and no voltage was getting past the switch in any of the three positions. We decided to just bypass the switch so we pried open the switch case, removed the corroded slider, and used a jumper wire to determine which output terminal was "On-Full" and which was "On-Low." After determining the right terminal we used a soldering iron to place a glob of solder bridging the input terminal to the On terminal.
|Switch Case Pried Back, Slider Removed, Solder Added|
---> "Fixed" (good enough) in about 15 minutes for free.