Better be a pretty beefy switch, as those heating elements are going to draw some current. You're better off using a heavy-duty relay to switch the power.

Seriously, you could burn your car (and possibly yourself) up if you don't do this properly. Just go to Radio Shack and tell them what you're trying to do. Chances are they'll be able to design this circuit for you, and sell you what you'll need.

Jay.

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On the road, currently:
'83 300D (German spec.) 168k mi. - - Wolfgang (tucked snugly away for the winter!)
'87 300D 375k mi. - finally went over to "The Dark Side"
'87 300TD 225k mi.
Cannondale 66cm CAAD5 w/Campy/Jamis Aurora
Hujsak Custom Fixie/Landshark Track Shark Custom/Ahearne Custom 29'er