alternator only option?
 

Car came home with all kinds of electrical issues. Found the battery dead. So I charged it up, and everything is fine. With the car running, and the lights and heater on full, the Voltage at the battery drops.
Pretty sure it is the alt. and no fuses anywhere that I cam see, So before I pull it out, ask the experts.

Thanks
Doug

Does your red battery light glow?

Check in the dark.

If so, a new voltage regulator is in order.

No, I have not checked it in the dark. Is the regulator part of the alternator on a 83 300SD?

Battery drains are difficult to track, yes, the alternator is dead, but it could need a simple Voltage Regulator for around $40
GET a multimeter and take some battery readings with the car off, key on, car running, and report back with what you find.

With the key off the battery builds voltage. The key on is the same as running for the most part, a slow drop, when the lights and heater is on, then the voltage drops more rapidly. With the car running should I be getting 14V from the alt? I just got it charged adn started looking at it.

most stock MB alts put out around 13V at idle... if you get 14 you're the exception.
anything below 12.8 at idle, and the alt/regulator is suspect...

post the exact voltage in the three positions I listed in my first question please. diagnosis is easier with numbers to follow...

at idle with the lights and heater on I was at 11.75, then after doing a few things, about 10 minutes, it was down to 11.5

yup. sounds like bad regulator as a minimum...

Thanks, I will get to work and get it changed and go from there.

Thanks again

It does not sound like the issue you have. Yet just in case the glow plugs are staying on just check for voltage being present at the plugs when it should not be. Only takes a few seconds.

The alternator cannot overcome their draw if constantly on and the voltage will sag. As stated I do not think it is your problem. Still should usually be checked as it takes so little to do.