Cadillac Repair: elactrical, rear defroster, belt tension

Question
I have a 80 deville 6.0 with a/c. The alternator is new battery new. It has 13.75volt charge but the battery is not charging. Well 1 minute seems fine the next it's dead. It seems like something is drawing way to much juice can't find out what. Also i put a new blower motor in a day or two before but it does'nt have be on for battery to die. The lights dim a little when i turn the blower on. Any ideas would be greatly appreciated.Thank you

Answer
Hi Dale, When running the engine is when it shows 13.75v on the meter? If you continue to run it does the voltage drop or stay pretty constant around 13.75v? Having the lights dim would be normal at idle when the alternator isn't charging at it full capabilities. Turn alot of items on like blower on high, headlamps on high and rear defroster on and bring the idle speed up to 2000 rpm or so and check the voltage output. It should still be around 13.75v. If not then the alternator or voltage regulator is bad. Double check the belt tension by trying to push on the alternator fan with your thumb. If the belt is tight then the fan should not turn. How long does it take for the battery to go dead? You might have left on a light or a computor or sensor might be staying on causing the drain. You would need to hook up a digital ampmeter to the neg. battery and cable to read what the draw is. Your meter should range from 5 milliamps to 20 amps and leave the key out of the ignition for this test. Hope that helps. Bill