The OP didn't use OE switches, no one did back then. The GD/GR seats are hog rings and tension wires, nothing is seriously glued. Most kits have a thermostat to regulate temperature, if the factory setup uses a relay it's most likely to avoid running high current through a switch.
Aftermarket kits are so very simple: ground and switched 12v, done. Tap off the cig lighter or add a circuit.