You can use the one Ford used, it's a little silver can on the back of any Ford gauge panel from '57 to well into the 70s. Called a constant voltage regulator, CVR, or IVR, you can get one from NAPA for a '67 Mustang, for instance, 12V in and 6V average to the gauges and grounded to the back of the panel, it's just a bimetal set of points, self contained heat (unaffected by ambient) works just right for any King-Seeley gauges. ..B.