It's an 83 Blazer, mostly stock. I don't have guages, just these idiot lights which are making an idiot out of me. So the battery light glows dimly. Not full on, just dimly and it's so dim it has to be night time or you can't see it. When all the heater fan or other accessories run, it's a little brighter. I checked some voltages with my $15 multimeter: 13.5-14 volts at junction block, 13 volts at main battery, 14-15 volts at alternator output, 13.5-14 at each of the other two polls of the battery isolator. Nothing runs off the aux battery and it's at 13-13.5 volts. All these are with the engine running. Turning on all the accessories doesn't seem to make much difference, maybe 1/4 volt. The alternator is a 78 amp one. This has been going on for a good 80,000 miles but the dim glow seems to be a little brighter now. It was also doing this before I got the dual batteries and with the previous alternator too. What should I do? What is causing this? The main battery, a red top, is a little old and reads about 12 to 12.5 volts with engine off with a nice 60 degree morning here in Golden.