Odd vibrating wipers on 72 C-20

[billdozer]

Hey guys, kinda weird question here. I've got a recently purchased 72 C-20 that was not getting power to lower portion of fuse block when I got it. Bad ignition switch was the culprit and now all the stuff powered by the brown wire to fuse box is working: wipers, blower, signals, etc. Hurray for that. But... now, when the wipers are in the parked position and the switch is off, the driver's side wiper arm nervously vibrates just a hair. Like it's getting just a little current maybe? It doesn't even move enough to scrape the blade on the glass, just jiggles around non-stop. It does this whether engine is running or not, as long as key is on (so switch is getting power). Does this sound familiar? I can fight loose connections, bad grounds, etc but kinda don't know where to start on this one. Bad switch that isn't quite breaking the connection? Any tips?

Thanks!