Harnesses Unlimited - custom auto wiring harness Battery cables for a 6 volt car should be at least 0 gauge or preferably 00 gauge with brass battery terminals and copper lugs at the body and starter motor. L) Why don't you do wiring for Ford Motor Company products? When we started all the other companies were making wiring for only Ford Motor Company products. Exact OEM Reproduction Wiring Harnesses for Classic Our wiring harnesses are brand-new and better than N.O.S. (new old stock) THE PROBLEM: Let's face it folks, NO automobile manufacturer ever designed a wiring harness to last 30-60 years. As a matter of fact, your vehicle's original wiring was only designed to last 10 years before it started to deteriorate! There is ample documentation to substantiate this claim.