Hook it up to the proper voltage battery, 12 or 6 (red wire to positive, green or black to neg.) get 2 same voltage bulbs. Touch the bulb end with one of the remaining wires , pull switch down or up an see if the bulb lites up. Same with the other wire(s). If you have a VOM, you can also use that instead of the bulbs. (set to DC voltage).
PS. you possibly will have to ground the side of the bulb metal to a ground (neg post on batt?, metal dash?.)