On a 79, when I start the engine, the alternator puts out around 11.5 volts whether or not the choke is engaged (from 600 to 1200 RPM). The voltage will stay the same as long as I don't touch the accellorator. If I rev the engine to release the choke or rev it after starting without the choke engaged, the alternator output jumps to 14.8 and the "GEN" light comes on and will stay in that area fluctuating only slightly (.5 volts) when I turn on the lights, radio, fan, etc.
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Re: Charging Voltage
Measure the engine off voltage with a multimeter. It should be about 12 to 12.5 volts indicating battery voltage. Then measure it just after you start the engine. It should be in the range of 13.5 to 14.5 volts. If it's low shut down the engine and "recycle" (remove the reinstall) the side connector; then restart the engine and check the voltage again. The side connector should fit very snug. If not you might have an intermittent condition that comes and goes with engine vibration. You can usually rework the connector to fit properly, but disconnect the battery first because the red wire is hot all the time. If the side connector is snug, it might mean it's time to rebuild the alternator with a new voltage regulator (assuming there's not an intermittent short circuit somewhere else that is dragging the voltage down). This is not a hard job for the DIYer and you'll retain the original p/n and date code. The toughest part is getting the pulley off without an impact wrench. One way around this is to loosen the pulley nut with the proper size offset box and allen wrench while it's on the car since belt tension will help keep the shaft from turning. Beyond this it's pretty straight forward. Just follow the service manual procedure. Changing the bearings is tough without a small press, but if they turn smooth just relubricate them. Change the regulator for sure, and run the continuity checks on the stator, diodes, and rectifier bridge and replace any parts that fail. Replacement parts from any reputable name brand manufacturer should be up to the task, but a heavy duty diesel mechanic friend of mine prefers the Standard Blue Streak product line.
Duke
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