OK---on the corvette, and others , wipers ar a completely different sort of device, especially since they continue to run to the park position after you turn them off---------


On an electric fan set up, that is an incorrect method of wiring, and the reason is because of the fans being able to induce some current into there feed wires since they are actively still hooked up----

You really need to wire it so the relay opens and closes the contacts for the live feed wire to the fan and control the circuit in the relay that closes that contact.

I understand that lots of situations will control the ground side of an circuit because the ampereage is lower, however, generally speaking, maintain solid , constant grounds to the chassis for the complete return of the circuit---