sounds like it's the switch that comes with the aftermarket electric wipers? check the switch for continuity with a meter, also insure the knob isn't just turning on the shaft .... might look like this? if you need a new one, may be available separately from some vendors or from Newport Engineering

Bill


Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot