Check the grounds by the headlights on both sides of the car. When my son and I installed the headlight relays on the car, he dislodged a ground wire from the right front ground point. The right hand turn signal would turn the windshield wipers on.

You may want to take the ground wires off and clean the connections and the chassis grounding points, and then check them in service with a voltmeter. To do this, with the voltmeter on volts, put one probe on a good ground point on the car, and touch the other probe to the upper electrical fitting crimped on the wire.