My wiper motor won't park so I set about to figure out why. Ran a ground from switch plate to dash frame - didn't help. Ran a ground from switch plate to motor mount - didn't help. This is as per video posted by Alan in post titled Wiper Motor Testing 71 Challenger from last fall.
I checked the firewall plug with a test light and I have power on the top passenger side terminal and the bottom passenger side terminal with the switch on. The bottom one is brightest on low speed, a bit dimmer on 2nd speed and dimmer yet on high speed. The top driver's side terminal had power with the switch off and the bottom driver's side had no power at any time.
I'm guessing the bottom driver's side is ground and the top driver's side is park. Is all of this correct?