Leather seats are installed!
First attempt: I was using the same power supply as one of my amps. Went well until I tried to start the car, and I killed a few Eng Cont fuses in the engine bay. Try again.
Second attempt: I ran the positive from the 12V cigarette output to the seats and the car started like a boss.
So thank you to everyone who gave me some ideas on how to do this. Now to clean up the old RS4S seats and sell them.