Can't find fast battery drain

[Kestas]

My car all of a sudden drains the battery. I had to charge the battery to get to work, then again to get home. When home I immediately did the drain test, placing an ammeter in series with the battery cable. I'm getting a draw of over 500ma. I pulled each fuse from the fuse box and a few sattelite fuses... still over 500ma. I swapped the battery - no change. What do I do now?

This car is a daily driver. No work was done to it recently. The wiring harness has been replaced.

[mbdoc]

Most likely draw is the antenna.

[HarryM]

Does this car have an aftermarket alarm? If it does, take it out and throw it in the nearest dumpster.

[blueeagle289]

I had a similar battery problem on my 92. after removing the trunk CD player. The radio system and/or the antenna were staying "on". I disconnected the whole system and the problem was solved. I am getting a new CD/radio for the car, replacing the whole original system. In your case,you may need to just check the antenna and fix that. Ben Carter

[Mike Murrell]

Originally Posted by HarryM

Does this car have an aftermarket alarm? If it does, take it out and throw it in the nearest dumpster.

I have a '91 300-SEL that's had a semi-slow drain since I bought it 10 yrs. ago. I got fed up with it and put one of those $2 quick disconnects on it. The car is used far less frequently than my others, so I don't care about having to monkey with radio settings everytime I restart the car.

I agree with Harry - the after mkt. alarm could be a problem and I know it's not in your case, but if you have one - shoot it. I'd bet a buck it's my problem, but my time these days is stretched, so I cannot thoroughly diagnose the issue.

I've called around about getting it disconnected and no one wants to have anything to do with it. Just as well I suppose since everytime I put a car in a shop, it comes back with more problems than it went in with.

[blueeagle289]

One thing I found in disconnecting my radio system was that the large control unit in the right trunk wall area was also had to be disconnected. In the 300CE that is where that apparatus was mounted. I have aerial cables going back both sides of the car, connecting to that complex control unit for the radio, plus the electric aerial on the left rear. I pulled that radio control unit totally out of the car and disconnected all aerial leads and power to the aerial from everywhere. That stopped the battery draw. Hope this helps a bit ... Ben Carter

[Kestas]

Okay, here is where I'm at.

- I disconnected all fuses from the fuse box, plus a few satellite fuses under the hood.
- I removed the alternator from the car.
- I removed the radio from the car.
- I removed the power antenna from the car.
- I removed the CD player from the trunk.

Yet I still have a massive power draw.

The car is bone stock, no aftermarket alarm, radio, or anything.

I'll start disconnecting the computers under the rear seat, and see if those are the problem. What else can I do?

This has me worried. I've read the number one reason for scrapping german vehicles is because of electrical problems. I'm afraid you guys may soon see an otherwise perfect E320 cabriolet sitting in the junkyard because no one can drive it.

[zcc]

What about the xenon lights if you have?

[bolomiester]

Put everything back and remove the starter. I'll bet your drain is through the starter solenoid.