heated seat

I own a 97 Eldorado. I would like to install aftermarket heated seats. For the factory heated seats, does the switch plug into a relay, or is it just wired to a single wire? In either case, what color(s) is/are this/these wire(s)? I would like to wire the power wire from the aftermarket kit where the factory switch would be wired to. The car did not come with heated seats. Thanks.