I buy them a dozen at a time on Ebay- - - - -about $4.00 apiece. They're also available with a 6 volt coil. Most of them come with the multi-pin plug and wires included in the price. I'm upgrading my motorcycle headlight system with a relay-operated halogen headlight today, and a set of passing lights soon, also through a relay. That eliminates multiple switches with a little resistance in every contact, and the voltage from the dimmer switch is only used to power the coils on the relays. Less voltage drop- - - - -brighter lights! I run a fused, heavy wire from the battery bus to a convenient mounting place close to the headlights to mount the relays, which minimizes voltage loss before it gets to the end item. Either 4 or 5 pin relays work- - - - -just clip off the wire to the "normally closed" contact.
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!