Let me draw up a circuit diagram and get back with a link shortly. It's the same relay that's used for fog lights, etc. Hundreds of 'em are available on ebay, cheap, but most of them are 12 volt, however. The same thing could be done with a 6 volt overdrive relay, however.
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!