[Oldgearz]

My A will run a long time on the battery alone as I have a red top battery. My alternator acted the same as yours and I took it to an alternator shop and they said it wasn't working at all. Regular car parts stores wouldn't even look at it because of 6V, positive ground. As Ken said, if you turn on the lights and get no response on the amp gauge other than minus reading (at fast engine rpm), chances are alternator is bad. The GM one wires are very finnicky about exciting a charge. After repair, mine will never excite at idle and lights or horn won't seem to excite a charge either. Only a few revs work, and then it stays charging until motor is turned off.