I have an intermittant problem with my 1992 Isuzu P’up. Saturday, I was driving home when the “battery light” and the “low fuel” warning lights went off, then my car stalled at every stop til I got home. My Dad and I checked the body ground connections. We disconnected a woven wire ground, reconnected it and the warning lights went off and the stalling stopped. Cleaned the connectors with crocus paper. This morning I drove to work fine. Driving home, the same lights came on again and it stalled at every stop. Tried the reconnect thing again and it didn’t work. We put a ohm-meter to the ground connections, zero resistance, fine. I took the black cable off the battery and checked with an ohm-meter, Zero resistance, fine. We checked the voltage on the battery with car off and car running with radio and lights on and it was fine (no voltage loss). The alternator should then be fine. Any idea what to check next? Does this sound familiar to anyone?
I’m not quite clear on how you concluded that the alternator is OK. The problem certainly sounds like a bad battery, bad wiring or a bad alternator. Over the years, I’ve encountered several cases where battery acid got into a battery cable and ate it invisibly under the insulation but that has always showed up as starting problems rather than low voltage in normal operation.
What I think is happening is that there is something wrong – alternator, battery, wiring that is causing low battery voltage. When you fix weak grounds or whatever, you make the low battery voltage a bit higher for a while. But whatever is making the battery voltage to drop is getting worse, so after a while, everything dies again. Since you have a volt-ohm meter, have you measured the battery voltage when things are OK and when they aren’t? Maybe that will tell you something.