Going To Ground
Q. I have acquired a very interesting and rare car which has a 12-volt positive ground system. The car was made in England. It is a 1952 Alvis TA 21 drophead coupe (to us Americans that's a convertible). The car has been stored in a barn for 47 years, and will need a cosmetic restoration as well as complete rewiring. The car originally belonged to my cousin who started restoring the car around 1961 and then abandoned the project, as he did not have the garage space. The engine has been completely rebuilt (less than 1,000 miles on it) as well as many new parts installed. This car would make a really unique and cool street rod, as it is aluminum bodied and has suicide doors. I would like to get the car drivable as an antique first, and then consider late-model running gear at a later date. I've already purchased a wiring kit, and a set of gauges for it (street rod application). My question is, what would be involved to convert the 12-volt POSITIVE ground system to 12-volt NEGATIVE ground?
Wayne Merrell
Via Email
A. Cool car, Wayne, and it should make a unique rod as you say. Apart from altering your battery leads to fit on the opposite terminals (the clamps are different sizes for positive and negative), and reversing the two wires on the ignition coil, you have to re-polarize the generator. To do this, first disconnect both generator leads. Connect a length of 14-gauge wire to the hot terminal on the starter motor or fusebox and flash the other end of the wire against the field terminal (the smaller terminal) on the generator, very briefly, but so you can see a small spark. Do not connect this wire to the generator. You may now reconnect the generator leads. A stock ammeter or voltmeter will require the wires switching around too. Windshield wiper and heater motors need no re-wiring. If you use an electrical fuel pump, make sure it is a negative ground pump.
However, if you are adding new wiring and gauges, why not add a modern alternator instead of the generator and just swap the battery cables around?