Basic Understanding of Relays?

hi Lee280zx, you can use a socket or terminals. The relays we typically use from Bosch are rated at 30 amps and Potter & Brumfield's are rated at 40 amps. You can purchase relays from your local car audio shop, auto parts store, and electronics supplier, among others. Normally Open and Normally Closed refer to the contacts on a relay. An SPDT relay will have a common, normally open, and normally closed terminals, as well as two terminals for the coil. You can find more info on SPDT relays here.  

You can either crimp,spade connectors on the wires and plug them onto the relay,or you can purchase the prewired socket to plug them into.  In my opinon you can make a neater harness by the crimp method.  Most relays are good for 30 to 40 amps.  The trigger (the wires on the coil) should provide at least 500 milliamps to energize the coil.  That doesnt draw anything(not enough to even mention). Always look at the relay and verify the amperage of it.    Most pepole use Bosh relays.  I have seen alot of diffrent brands but I would guess that the same company probably makes most of them.  To answer your last question, I just ordered some relays from www.partsexpress.com and I got them for $1.89 each.  If you have any more questions feel free to e mail me directly.  Brian