I've been working pic's to show you whats going on, it's to late LOL therean easy fix, take less time than the drive to ye ol repair person ..
the screw driver in the slot
tweak and bingo..
some do have screws
ok inside, there maybe mounting screws on the corners or this one is under the wiper arm.. it's easier to remove the block from the housing ...
you see springs and the reviets, that wiper must touch each reviet as it pasts over ,, each one contorls a different speed, clean those and under the wiper ...
next at each reveit and on both side you'll see a hook that attaches the spring, remove the springs end and clean those, should a spring be screwed up on the end strecth it to fit and cut off the old end. if it's burnt in half you can use any spring thats even close to that size,, worst case cut the weak section of spring out twist there end together and install,,, put it all back together less the cover ,, hold upside down plugged in and power up the motor.
look for glowing at the hooks, sparks. SMOKE and do this a few minutes to feel for heat on the housing ,,it should not even get warm you get any of those, you still have a dirty contact at the hooks,,,
by doing this you'll get the picture on how these pedals work ,, should that block be broken glue it back together ...
don't worry your not going to get shocked,,,, I would not spill beer in it or stick my tounge on the brass contact,,, if you have a multi meter that will do Ac current you can use that to test it
you will be taking it apart and back together about 3 x's to get it right ..
these are two different pedals ,, this one shows how the reviets get so woren they will have to be silver solder and filed smooth,, the reviet closest to the wiper is all but gone, the next two are very bad,, this pedal works on the top half of it's speed control.
the other pic's are all the same pedal, it worked much like yours, the problem was at teh hooks plus someone in the past did there fix and streched the hell of there springs all at the end
yes spring lenght matters in a perfect world.... 90% of the time you are going to get some humming at a slow start up.. play with it and it will work ......................... better LOL