Not sure how to test the switches with a multimeter though
If the switch has 2 wires - turn the battery on, put the car in reverse and back probe the harness with a pin or similar and check for voltage on both wires. If you have voltage on both the switch works. If it's a single wire switch you will need to remove it, depress the switch manually and check for voltage on the threads on the exterior of the switch. Again if you have voltage it works.
