I've got a 1980 300SD that is discharging the battery while running.

First, I suspected voltage regulator on the alternator and even though the alternator bench checked OK, I replaced the regulator anyway. It was relatively cheap and easy to do. Battery (newish and tested good) continued to discharge enough after my 30 minute drive to work to not have enough juice to start the car.

I swapped out the MB alternator with a GM alternator that I had an knew was good. That was pretty easy and it was a little higher amp anyway. Still the battery drains. So, I fired up the car, put an amp guage inline with battery cable and I can see that it's pulling a lot of amps.

I pulled off the power to the glow plug relay and the pull on the battery dropped by a bunch, but it's still pulling more than the alternator can put out. I have no blown fuses. I have removed the climate control servo under the hood and just put in a hose and ball valve for my heater.

What else, besides the glow plugs, could be pulling so many amps to drain my battery over the alternator output?

Thanks!