Windshield wiper blues

Hi
I have a 1990 Buick LeSabre with a 3.8L V-6 engine and a 3 speed pulse type windshield wiper system. Occasionally (and mostly when it is raining!) the windshield wiper will stop working! Sometimes if I change the speed to high they resume operation or if I turn them off then back on again they will resume operation. However. lately they will not resume operation no matter what I try. Then a couple of days later they will work fine! Can anyone help me find a wiring diagram for this wiper system? And does anyone know of GM's with similar intermittant wiper operation?
Thanks

You may have a marginal ground where the windshield wiper motor is attached.GM products are known for this and I did have this happen to me. When they're not working, turn on the wipers and try attaching a jumper wire (any wire will do) from the metal casing of the motor to a good ground on the vehicle frame. Then see if they come to life.

Relays can be finiky as well.