removed accel unit from pedal. microswitch was misadjusted and did not interupt contact.readjusted it and now clicks at first touch of pedal and hum is gone in forward or reverse.
hum starts when pedal is first touched but then contactors drop out within 1/4 second so still no go.
doesn't look like accel unit was ever tempered with as white paint on screws still intact on circuit board and microswitch.