Ask the Mechanic

Famous "6 to 12" Volt Talk

(Photo illustration by Barry Falkner)

READER: I have an old C Farmall with a distributor that came from the factory with a 6-volt, positive ground system. Like many of the older tractors, for some reason, it had a positive ground rather than a negative ground. I am converting the tractor to a 12-volt system in hopes of getting rid of regulator and generator problems.

I know from some of your earlier columns an alternator will not charge if the battery remains positive ground, so could you give me a few more details on how I should go about completing this conversion?

I don't want to fry the ol' guy. We have been together a long while.

STEVE: I am glad you two are still together. The first thing you need to do is get a small 12-volt battery that fits the old 6-volt battery compartment. I recommend, as far as an alternator goes, a one-wire alternator.

Next, run the large single wire from the alternator to one post on the amp gauge, and from the other post, run the wire to the starter solenoid, where the big wire from the battery positive post will now be placed. This will put the charge back in the battery from the alternator. If the charge shows backward (negative) on the amp gauge, switch the two wires on the amp gauge.

Then, from this same post on the solenoid, run a "hot" wire from this post to the ignition switch, and from the other post on the ignition switch, run a wire to the new 12-volt coil with internal resistance to the positive (+) post on the coil.

This is opposite of where the original wire from the switch was on the coil. The other wire on the coil goes to the distributor.

Have fun with the ol' guy. Old tractors will live forever and seldom have a blinking light on the dash.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


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