Switches don't care what voltage they're used with. The headlights should be marked for voltage, but if they're not, try putting 6 volts to one of them. If it's normal brightness, it's a 6V, if it's very dim, try it on 12 volts. A relay can be checked with an ohmmeter, but you'd need a known good relay to compare with. Generally, a 12V relay will have about twice the coil resistance of a 6V relay.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!