[ray_mcavoy]

I agree. Although there is also the possibility of a bad connection in the wiring.

On the 1977 & older wiper motors, the switch grounds both the "low" and "high" terminals for low speed operation. It only grounds the "high" terminal for high speed operation.

So a bad connection between the switch & motor in the "low" speed circuit will result in the motor running at high speed on both switch settings.