96 e300d battery drain
 

Hi Guys
My battery goes 12.50 v to 12.12 over night . New Battery. I took the battery out of the car stays at 12.50v overnight. I used my meter It says a 573 drain ( were does the decimal point go ? ) I took out the fuses stayed the same . I removed the wires from ALT. same. Were:confused: should I look next ? It sparks at the battery post. Thanks Greg

Your car has 3 fuse boxes -- did you pull ALL the fuses?

Actually there are 4 fuse locations in a W210
- Main under hood - left side rear corner - misc items in the front of the car
- K40 relay in the electronics box - right rear corner under the hood (the box that says "battery under rear seat") - engine electronics
- Sail panel on left end of dashboard - exterior lights
- Under right rear passenger seat by the battery - misc items in the rear of the car

You're on the right track with the meter in series, sounds to me like the "573" is 0.573 A or 573 mA. That would be about the right amount of drain to pull the battery down 0.4 V overnight.

You can rule out stuck glow plug relay or ABS pump relay, those draw way more than 573 mA.

Any electrical modifications to the car?

Not as simple as pulling fuses!
 

The W210 has complicated computer and communications systems so pulling fuses to find the problem, as one could do on older cars, generally doesn't always result in problem discovery. The car's communication and computer systems are interlinked and stay active for some time even after the car has been turned off and the doors locked. As you can guess the security and door lock systems also remain active. To add an extra layer of complexity the communication and computer systems can "go to sleep" then automatically "reawake" hours later and draw down battery voltage .... which makes for intermittent problems over time .... which can be super tough to diagnose. But all is not lost .... usually electrical problems leave "clues" for you to trace. In my 1996 E300D I had a similar problem where the car had to be driven every day or the battery would go dead .... my mechanic couldn't figure it out. However, one day when I was washing the car I heard a slight buzzing out of the right front speaker even though the key was out and the radio off. That was the clue I needed. Ultimately, it was the Bose Amp that would intermittently "turn itself on" in the middle of the night for a few hours at a time running the battery down. I replaced the Amp with a used one I got from a junkyard listing on e-bay and everything was good again. I've since discovered by reading other posts that this is a common problem with the Bose Amps. Another common problem is a minor short in the alternator. If you have an older alternator you might want to check it out to make sure the diodes are functioning properly. There are also the traditional problems such as the trunk light or glove box light remaining on because of a switching problem. I've also read of problems with seat controllers not turning off or ignition switch issues not letting the computer systems "go to sleep". Good Luck on your search .... it may take some time and effort but if you have patience your car will drop a clue or two for you to zero in on the problem!

Good call on the Bose Amp

I have heard of leaking trunk seals causing water to drip on the connector for the amp, causing the amp to short out.

You mentioned that you removed the wires from the alternator. Just wondering did you remove all the wires including the large one to the battery?? I had a similar problem with my car, and it turned out to be a failed diode in the alternator. Good luck...........