What's wrong, what should I do?

[dirtynails]

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.

 

[diesel4me]

a few causes...

Usually a dimly glowing alternator idiot light is caused by one of the three diodes in the diode trio inside the alternator failing..it'll still charge,but it won't reach its rated output--thats why it glows brighter as the loads increase when you turn on lights,heat,etc..

Bad grounds can cause a feedback that will dimly light the idiot lamp also..so can a short curcuit in the wiring,when one wire melts and lays across another,making a connection between the two..printed curcuit board in the dash too,can be a source of feedback if the foil "wires" rub to ground or another "hot" source of 12V..

I've had a few 60's and 70's GM's that had the glowing alternator lamp syndrome myself..after an extensive investigation of the wiring,rebuilding the alternator,and adding ground wires with NO improvement,I decided to say "F" it,and as long as the battery didn't go dead,to just IGNORE the dam light!.

I never got stranded with a dead battery,but I'll admit it made me quite uneasy when driving to upstate New York a few times,where about 1 person lives every 10 miles or so... ..never did find out why the lamp wouldn't go out completely..I suspected the voltage regulator,since it is what controls the lamp (the 12v it applied to both sides of the bulb is supposed to put it out after the alternator starts charging--but I tried 2 different alternators,plus the rebuilt,and nothing changed!.

 

[dirtynails]

Thanks, that's good info. I've already improved the hell out of my grounds, changed alternators put in the second battery so I will have one if the primary goes and right now I quess I will just say the hell with it untill some day I accidently find the culprit.