Best way to check a switch is to take it out and measure with a volt ohm meter (multimeter). It should have continuity one way and not the other. Doesn't matter if it's normal open or normally closed switch. It's best to do this with a sweep arm type rather than a digital one as the digital ones have a delay in them whereas the sweep arm type you can see if the switch break/make is clean or not. This is also more useful when checking potentiometer type switches (like fuel sender) where you can see if the sweep is smooth or not. These sweep arm voltmeters are cheap and can be picked up on sale from time to time. Just saw one at Lordco on the tools for sale bin by the door day before yesterday.
If the switch is fine and you have a light on constantly it is either out of adjustment or the wiring is shorting to ground before the switch.
If the switch is fine and you get no reverse light, it is either out of adjustment, your bulb is burnt out (check with multimeter not by eye), the bulb socket is dirty, you have a dirty connection in the circuit or the wire is broken somewhere in the circuit (may be broken wire with in the insulation and not visible to the naked eye).
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