Haven't gotten around to dealing with mine yet, but if the original motors are good, I'm going to use a voltage reducer to get it down from 12 to 6 volts. If the motors are bad, I'll replace them with 12 volt ones and get the 12 volt repro switches. I'm debating whether to use separate switches for the heater and defroster or just run them both from the same switch, but I guess using two switches would be the best bet.
As for fuses, I'm planning on using 20 amps which is what my trucks uses for the heater.
