Charging lamp stays on when Key is off

[psy4s]

I have a 1992 E30 325ic. The Electrical System Charging lamp stays on when the key is turned off. If you started the car it would go out. You could not leave the radio on for more than just a moment without the battery going dead. Now I went out this morning, and it was totally dead.
Background on the car, for a little while the heater blower has been hit or miss, but when it did work it only worked on Hi I figured this was the resistor or blower motor. The Cruise just quit working all together. I followed the wires to see if there was something unplugged, because I replaced the Dash pad last year, but I did not find anything. I am not real concerned about the blower and the cruise, but I need the car to run, because it is my only transportation at the moment.

[Manolito]

I have not looked at the wiring diagram, but I suspect that the most likely cause of the light staying on is a shorted diode in the alternator. With Bosch alternators of that vintage, the ground strap on the alternator can be a problem, but I don't think that would cause the light to stay on when the car is off. Anywhere that sells batteries (e.g. Sears, Interstate) should have a tester that will quickly identify an open or shorted diode.

They used to test charging systems for free in hopes of selling a new battery. Not sure if that is still the norm.

It would not be too hard to replace a diode in the alternator. The hardest part would be finding the correct diode, since auto parts places will sell only the complete rebuilt alternator, and the diodes are generally sold only in bulk to the rebuilders.

The rebuilt alternator is about $150 on line, and comes without a pulley, so you have to pull the pulley from your old alternator.

[Frajo]

When my cruise went out the culprit was the SI board.

[Jared at Pelican Parts]

Manolito is right.

The first thing to do is to check the battery at your local auto parts store. Most places will do that for free.

After that, then it's the diode.