Been down that road, as a lot of us have had the same or similar problems. I admit I read every Klaus post but I must say my experience with short drives differs completely. My '96 has 170k, about 60% or more are trips of less than 30min and less than 25 miles with the car sitting afterward from one day to 7 or more days without moving. And the headlights have been in the on position since 1995 purchase. Never been in the off position when the car was moving. I think I am on my second, maybe third battery in twelve years.
My hunt for "black voltage" led me to the door posts lamps. Look just below the door latch strike area on the end of the upholstered area. I think they are activated by the door handle and deactivated by the striker bar hitting the door latch mechanism. Mine were not being deactivated and remaining on constantly. Try this test. Open the door. The lights should come on. Use a screwdriver or whatever to move the door latch to the closed position as if the striker bar had hit it. The lights should extinguish. Check all four in this manner. If they do then that can be eliminated as your source of dark voltage. If not then remove the bulbs from the four lights or else have the door latch assembly replaced. Remember to reset the door handle latch to the open position after the test or else the latch will hit the striker bar. Pull up on the handle and pull the latch back to the open position with the screwdriver.
Hope this is of some value. I went through an alternator and two batteries plus several jump starts before I traced it to the door lights.