Dirty voltage regulator points, probably. With the engine running at a fast idle connect a jumper wire from the "F" terminal (at either the generator or the regulator) to ground, and see if the ammeter needle jumps to full charge. If it does, remove the regulator cover, disconnect the BAT wire at the regulator, and give the 3 sets of points a good scrubbing with a piece of business card or a slice cut from an index card. Reconnect the BAT wire, start the engine, and check to see if the ammeter deflects to the + side. DO NOT USE SANDPAPER OR A FILE ON REGULATOR POINTS! They open and close with a slight wiping action, and scratches, even tiny ones, will make them stick.
Jerry
