> These sound like an automotive version of the cathodic protection systems used on petroleum pielines and the US Coast Guard's 110' patrol boats.  I'm sure similar stuff is used other places but these are the ones I'm fairly famaliar with.  Basically the idea is to balance the 'charge' of the hull or pipeline with the 'charge' surrounding material to prevent electrolysis.

The important thing to note about this is that both pipelines and boats are constantly immersed in an electrolyte.  Cars are not.  Short version - won't work on cars.  I'm commented on these systems previously in the archives.

Keith Adams
Calgary, Alberta, Canada
1986 Vanagon GL Westfalia "Roxy"