I have a reducer I bought from Carpenters to reduce my voltage to my heater, the instruction shows that you wire it in series to the accessory you are trying to reduce.My question is?, my heater has 3 wires 2 to heater and 1 to ground, this unit only has one wire you would add to it. Also when I put 12 volts to the unit I wasn't getting the 6 volts out, is this actually a potentiometer and works on resistance?

Claim to fame is the car was used as an extra in the movie Diner with Micky Rourke, Steve Gootenburg, Paul Riser and Kevin Bacon.