It's a long shot, but is the original radio still in the car?

__________________
'89 260e (212K Mi.), '92 400e (208K Mi.), '92 400e (not a misprint) (146K Mi.), '95 C220, '81 240D--Sold

It's aftermarket, and maybe failing. I'll try disconnecting if can't come up with anything else.

Sent from my D6708 using Tapatalk

My 1994 E320 Wagon had the same problem in regards to battery drain issue. Checked all the fuses in fuse box and all good. I was stumped so I went to auto shop today to have the battery drain issue checked out. The waiting was brutal while going through my thoughts of what went wrong. Bad wiring, short somewhere, fearing the worst scenario. 10 minutes later, it turns to be a BAD FUEL PUMP RELAY, part number 001 542 9619, located behind the battery on the side of the ECM (Electronic Control Module). Although the 30 amp fuse was good but I felt the relay was rather hot after I removed it. I asked the shop owner how was he abled to find the problem so quickly? He smiled and said that is my secret!!! Made my day. I ordered a new fuel pump relay today.