[OrrieG]

You can also use a volt meter to test the circuit thru the switch. You will have a ignition start hot probably from the switch and a paired output that is not in park and neutral but dead in R or and gear. The other pair will have a hot for the back up lights and a paired output that is hot when in reverse. If you aren't powered up you can just check for continuity with the ohm meter function thrugh the various combinations (4x4 = 16 possible combinations).