Trouble with wiper motor

Could be anything. The brushes in any of the wiper / heater motors were never designed to be serviced. You have a shop manual for your car? Otherwise I can post some info for you. These are a PITA to troubleshoot without a manual because of the way the switching works, the poor documentation, and the different motors/ switches.

Standard "quickie" checks apply.

Check the fuse and check power in/ out of the fuse

Check the switch is tight and grounded. Leave the key off and twist the switch vigorously through it's range several times.

Turn on the ignition, turn on the switch, and tap the motor lightly with a hammer/ mallet, etc.

Wiggle / remove/ inspect/ install the bulkhead connector