Were the plates electrically isolated? You said you replaced the rubber washers with nuts. If the nuts were metal, you'd have a direct short, or at least a very low resistance that could melt almost any cable. The plates need to be electrically isolated, about 1/16" (.06mm) apart. It is best too to have neutral plates between the electrcally active plates. The neutral plates will add resistance to the circuit, & reduce amps.
1998 Ford Ranger 3.0 liter V6
Modified Smack design installed 6/20/08
Modest gains of about 1.5 MPG (17.8 to 19.3)
No sensor controls (yet)