Ask the Mechanic

Why the Change

(Getty Images, Photo illustration by Barry Falkner)

READER: Why did manufacturers change from a positive ground 6-volt electrical system to a negative ground 12-volt system?

STEVE: It was found that with the negative ground system, corrosion on battery cables and points of ground on the vehicle were a real problem.

Old cars, trucks and tractors with positive ground systems always seemed to have fewer corrosion problems on connections than today's 12-volt systems.

A 6-volt system was also found to produce more corrosion in the electrical system, because the 6-volt system requires more amps flowing through the wires to produce the same power as a 12-volt system.

Since a 12-volt system can use smaller wiring than a 6-volt system, it was cheaper to build cars and trucks using smaller wire.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.