What kind of reducer? A 6v motor on 12 volts without reducing will last about 20 seconds before it's toast. Most reducers do need a load. Put the reducer in the positive line before the switch so the original switch also gets the benefit of the reduction. Read the part in yellow here..

http://devestechnet.com/Home/Native12VUpgrade#heatersystem


Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet