I purchased a boat that appears to have the running lights wired improperly.The switch center position-all off, up position-is bow lights only and oddly the removable rear light is in the switch's down position while turning bow lights off.
Clearly it is either incorrectly wired, or the switch has stopped working properly. Original owner no longer living - may have done wiring himself.

Can a bad switch cause this? This is south Florida so humidity may be a factor. Suggestions on how to diagnose the wiring. Would you cut the wires at the switch and tone them for identification like audio wires, or is there a better procedure with power accessory wires?

Thanks. Alan