Hello everyone!

I was hoping some of you could help me diagnose/find a problem I am having on my 1980 450 SL. From my limited knowledge of cars and electrical systems, it appears to be a short or current draw, but beyond that I really have no clue. The car was my every day driver for nearly a year and a half, and I didn’t have any problems with it, but when I bought a new car the 450 sat for nearly 9 months or so – and that’s when the trouble started.

When I went to jump the car, it started…no problem at all. And when I drove it around some and tried to start, it seemed to start up just fine. I drove around for a few days with no problems at all, but then as soon as I let it sit for a day or two, the problem starts over again and the battery is completely dead.

I took it over to Autozone to have them do a systems test, and the battery and alternator seemed to be working just fine, so I believe my suspicion was confirmed…that I have something drawing on my battery.

The first test I did was disconnect the positive terminal on my battery and use a multimeter to see what as going on. The first few times I tried this I was showing a small current draw, which appeared to be 7 or so mA, with an increase to 10 mA or so every second as the clock was ticking, I assume.

I went to check and see if I could find which fuse was this was coming from, and when I did this, I got the same reading from the #1 fuse, and nothing from any of the other fuses, so it appeared that the culprit was the #1 fuse.

Then yesterday I went to check again and see if I could delve into the problem some more, and when I started working on it, I was getting the same reading, with nothing unusual going on. Then, all of a sudden, when I checked the #1 fuse, my multimeter jumped up all the way to the end of the scale, so I switched it to the 20 Amp reading but was getting no reading whatsoever. So I was getting a monster reading on the 500 mA scale, but none on the 20 Amp scale. At the same time, I noticed that the light underneath the glove box, that turns on when the door is opened, suddenly turned on when the passenger door was opened…Previously it had always worked for the driver’s door, but not for the passenger door. I started playing with the black switch on the door that depresses when the door is closed, and it looked like it was a loose connection, because depending on what position or angle I was pressing it it would turn on or off. The other weird thing about this was that when the door sensor WAS working, I was now getting a reading of about ½ amp or so on the 20 Amp scale (but when it wasn’t working, I was getting NO reading), but when I put it back on the 500 mA scale, it was still reading past the scale.

So basically, I still have no idea what is going on. I am assuming my problem is with the #1 fuse, but beyond that I really have no idea, or no idea where to start to look. I don’t know if the door switch has anything to do with it or not, or what to do test the other components. I know this explanation is long and pretty basic, but I was wondering if anyone had any ideas of what I may be seeing, or any suggestions for me to try that may be common problems on the 450sl.

ANY help that anyone can give would be GREATLY appreciated!

Why don't you try removing the bulbs for the interior lights (remove the suspect consumers) and see if the problem goes away.
Gilly

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to add to what gilly reccomends you should also try disconnecting the A/C servo valve, it may be stuck and not able to return to the Park mode. i would suspect this even more if your A/C or heater is not working properly.

But would that draw with the ignition off?
Gilly

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Yes. It is trying to park and can't if it's frozen. I would also check the antenna.

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Thanks guys. I'll definately look into that. The only thing is I don't know anything about the A/C Servo Valve

Do you know of any good documentation online that I can find that will give me some more information on exactly what I'm looking for, etc?

Thanks!

You can unplug the two connectors on the servo to see if the drain disappears. If that is the problem, don't replace it. Buy the electronic replacement offered on Fastlane. It is a bit of an investment up front, but worth it in the long run. The climate control and the left front wheel folding up are the only two design flaws in that car, and the left front wheel is warranteed by MB regardless of age and mileage. The 80 450SL is a fine car. Sure the 380SL and 560SL are better, but look at the price difference.

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here is a picture of the unit. there are two plugs below where the vacumm lines connect, it is usually the left one that causes the draw

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