The general answer is two things:
One is the label.. Sometimes a 12 volt fixture will not be able to handle the higher voltage, Switch gaps are too small or insulation not thick enough.. Or in the case of a 120 volt fixture the current handling is not enougn After all 1 amnp at 120 volts is 120 watts. that's one BIG light. but at 12 volts it's only 12 watts. a dash light is six.
But the big item is the bulb.
So yes you can re-pourpose most 120 volt fixtures by using 12 volt lamps.> BUT. once again,, You have to have the right "Base" (the part that screws into the fixture on the bulb) the standard base, like a good old fashion 60 watt bulb, you can get those in 12 volt as well..
Frankly.. I like the selection I get with 12 volt fixtures better.
