I have an 83 300D Turbo. It apparently has a voltage leak, the car has been sitting up for a good while, I start it occasionally just to keep things moving. I noticed yesterday that when I turned off the ignition switch the alternator light stayed on even with the key removed. A day later the battery was flat. I bought the battery three weeks ago so I don't think it is a bad battery. I think something is stuck. I also noticed that the glow plug light didn't come on when I started the car.
Ideas? I am trying to sell the car and would like to get it fixed before inflicting it on some unfortunate soul.

Thanks,
Ben

It would seem that you have a bad ignition switch, or a short in the ignition switch wiring.

The light staying on with the key off is a symptom of an internal problem with the alternator. Probably a bad diode.

This means that the alternator is not charging consistently, or at all.

I had exactly the same symptoms aa you when my alternator failed from a bad diode. In my case the alternator was not even two-years old, from a reputable rebuilder.

The preglow relay is likely not activating because the battery voltage is too low.

The diode is not a DIY job.

A bad diode wold suck the life out of the battery, but it wouldn't cause the indicator light to go on. This is a bad ignition switch.

As above you will find that the alternator as a short circuit of the possitive diode[s] This is from the workshop manual ... Get the aternator output checked . If no out put, alternator is shot.

Either a bad key switch or bad alternator diodes can cause the battery to drain when "off".

Consider how a bad alternator and good key switch could cause the "BATT" lamp to light. The lamp's high-side comes from the key switch so would be "open". But, other components feed off that key terminal, so there is likely a path to ground on the bulb high-side when "off", say thru other dash bulbs. I don't have a schematic in front of me.

As mentioned, few here try changing the alternator diodes (6 big ones, 3 little ones), instead they just buy a rebuilt alternator. Your other symptoms (no charging) point to the alternator.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I believe if the the Alternator Light is still on with the Key removed and it is an Alternator issue if you disconnect the Alternator Electrical Connector the Alternator Light would go out.

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84 300D, 82 Volvo 244Gl Diesel

I was thinking about this...I assumed, as I think we all did, that the switch opens the indicator light circuit when the key is removed. But there's no reason that the lamp couldn't be switched to ground when the switch was off, similar to the way the window switches work. If this is the case, the light would be on if a positive diode was short. So it's worth testing the alternator.