Vintage Cars: 280CE MB 1978 European model battery draining, cigarette lighters, central locks

Question
Car's a treasure, love it.  1978 CE from Germany.  Gas.  Looked after it like a baby.  120,000 miles - odometer stopped a few years ago (is this difficult to fix?).   A few weeks ago the car wouldn't start; dead battery.   I had a new battery installed.  Dead again after the car stood for a day.  I'm told something is causing the battery to drain if the can stands day or two. What's the most likely reason.   (PS:  A few years ago the AC stopped cooling.  This draining battery only happened very recently.  I have heat and the system runs fine.  I'm told it's the compressor).  The people who take car of my routine maintenance told me to go to a MB shop. I'd like to know what the problem might be and the cost to check it out and fix it.  Love love love the car. Driving it every day to be sure battery doesn't drain down.  Thanks for the expert guidance on what to do!!

Answer
the most common cause is a ground short that is drawing amps from the battery.  I suspect it is in the interior lights or trunk, license plate light .  Do  these work?  If not just dont assume a bad bulb , could be a short. The other culprits are radios or auto antennas , that are suppose to turn off but do not.. rare , but it happens
The real way to check is to go across each fuse link , with the car off and see if you are getting an amp draw.  There is a 99% chance that the draw is from one of the fuses that stay alive when key is off[radio antenna.central locks,courtesy lights etc.]pull those one at a time while watching the clamp-on ammeter that should find it pretty quick.
Also look to make sure nothing is shorting out the cigarette lighters, coins ect can cause shorts


AC - could be compressor, could just be low on freon. IF the compressor is "wet" then it is probably bad, could also be simple like a fuse or relay...


Good Luck
Ron