Elec Short in 350SL: Where to Look?

[350SL4spd]

Hey guys,

I have a pretty major short in my 72 SL. With the ignition off I can watch the voltage in my battery drop: from 11.5v to 10.9v in about 30min.

Do these cars have any particular parts of the wiring that tend to go? What's a good place to start looking? Any advice on tracking it down?

I just put the entire interior back in the damn thing too...

[DieselPaul]

Like every ground in the car goes to the passenger foot well near the door hinges above and to the right of the fuse panel.

[350SL4spd]

Hey Paul,

Thanks for the response, but I'm confused: How would a dirty ground draw the battery down with the ignition off?

[RadioTek]

Have you checked that your battery is good? When charged up, it should have about 13.5 volts. A shorted cell will give you less voltage, and dropping.

If you know the battery is good, the way I would chase this is to put an ammeter in series with the battery, to see how much draw you have. Start with a high range and decrease. If it shows an amp or two, you probably have a failed device of some sort. If it is quite a bit more, then I would look for a bare wire or pinch.

To locate a bad device, pull every fuse from the fuse box, taking note of which color fuse goes back where. Take a notepad and pen in with you. Check the draw on the ammeter, you should be down to nothing on the meter, if something has failed. Then replace each fuse one at a time, until you find the 'spike' in your current draw. That would tell you which circuit is the guilty party. Depending on what devices are on that circuit, you might have to disconnect each one at a time to get the exact culprit.

There have been reports that the Becker radio that comes stock on the cars has been known to fail this way, but don't get fixated on that. You could have anything from a left-on parking light (the headlight turned one too many notches to the left), to a fried diode in the alternator.

Don't forget to eliminate the 'simple' stuff, first. It can save embarrassment. Like the time I spent a week chasing a 'no start' problem, only to find out that I had the car in Drive.

Good luck,
Scott

[350SL4spd]

Hey Scott,

Good idea to put the ammeter inline with the battery. I'll try that.

Battery is brand new. No radio in the car right now. It's an early euro with no power windows or anything, so I don't have that many things to check, but still a long process...

[DieselPaul]

Originally Posted by 350SL4spd

Hey Paul,

Thanks for the response, but I'm confused: How would a dirty ground draw the battery down with the ignition off?

Not sure, I misread your post, I thought you were asking where the majority of the wires in the car are. However good grounds and the key to a good electrical system. Probably still worth a look.

[nobby]

Originally Posted by RadioTek

Have you checked that your battery is good? When charged up, it should have about 13.5 volts. A shorted cell will give you less voltage, and dropping.

If you know the battery is good, the way I would chase this is to put an ammeter in series with the battery, to see how much draw you have. Start with a high range and decrease. If it shows an amp or two, you probably have a failed device of some sort. If it is quite a bit more, then I would look for a bare wire or pinch.

To locate a bad device, pull every fuse from the fuse box, taking note of which color fuse goes back where. Take a notepad and pen in with you. Check the draw on the ammeter, you should be down to nothing on the meter, if something has failed. Then replace each fuse one at a time, until you find the 'spike' in your current draw. That would tell you which circuit is the guilty party. Depending on what devices are on that circuit, you might have to disconnect each one at a time to get the exact culprit.

There have been reports that the Becker radio that comes stock on the cars has been known to fail this way, but don't get fixated on that. You could have anything from a left-on parking light (the headlight turned one too many notches to the left), to a fried diode in the alternator.

Don't forget to eliminate the 'simple' stuff, first. It can save embarrassment. Like the time I spent a week chasing a 'no start' problem, only to find out that I had the car in Drive.

Good luck,
Scott

It's great having you on the various boards, Scott.

[350SL4spd]

Man, this s*#t only happens to me...

I double check my brand new battery today and, completely disconnected to the car & just off the charger, it was dropping 1/10th of a volt every 8 seconds.

Pulled the battery off of my currently out of commission 300E and no voltage drop hooked up to the SL.

I'll chekc voltage again in the AM, but it looks like a bad brand new battery....

[RadioTek]

Get the battery tested on a load tester. The only way to get a really acurate test of a batteries' health.