Bob,

Not so long ago there was a thread on this about "battery drain".
I see you have a W124 T as I am (mine is a 300TD turbo).
These aging wagons are in particular vulnerable in the wire harness going from the clamp (socket) at the inside of the left hinge of the rear door. There are 24 screws on it interconnecting 12 wires. They get tired over the years by flexing thousands and thousands of times. So sooner or later some of these wires get broken and/or damaged insulation.
Some of these wires are "hot" because fed by fuse C : the central locking system and the rear interior lights. So trouble there could cause a lot of different problems : power drain, short circuits, failure of rear wiper, not functioning of rear washing fluid (pump is fed through wiper motor), central locking system, closing assistant failure, rear interior lighting, warning light
"lamp failure" on (with two new bulbs in the licence plate lighting)...and a lot more !
BTW do a search on W124 central locking system. There is somewere a very good explanation with pictures and diagnose. The vacuum pump you'll find it under the upholstery of the right rear seat in a big rectangular soft foam box. Try a search for the power drain too.
Good luck and keep us informed,

Danny