Q: How to tell if wiper switch or wiper relay is bad to fix wipers not working.

If you suspect the relay, power the relay solenoid directly with twelve volts. Then check for continuity across the relay switch contacts. If no continuity, as the solenoid is powered, then the relay is bad. If you suspect the switch, simply turn the switch "on" and check for 12 volts from the switch output to any body ground. If 12 volts are not measured, then the switch is bad. If there is a failure in the circuit, a Mechanic would trace it, using the wiring diagram in the Factory Service Manual, find the wiring, ground, termination or device fault that has caused an interruption in power and repair it. If you want the required steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an electrical circuit/component diagnostic and the responding certified mechanic will get this resolved for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.