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chocolate brown 1974 Mercedes 450SL
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Discussion Starter #1
I've searched the forums and haven't found a post that appears to address this issue. My sister gave me her 1974 Mercedes 450SL roadster to sell for her. Everything seemed to work relatively well when I first got it, but now several puzzling electrical problems have started. A guy in an auto parts store said that old Mercedes' were notorious for having electrical problems and that it sounded like a grounding problem. Any truth to that? If so, should you fix a grounding problem yourself (and if so, how?), or should I take to my Mercedes mechanic? Here's the blow by blow, but please see attachment for pictures of the engine compartment, which might help.

1. When I replaced all 4 headlamps recently, a friend of mine verified that the driver & passenger side lamps came on when I had low beams selected and that all 4 headlamps came on when I had high beams selected; however, now when I have low beams selected, none of the lamps illuminate on the passenger side (making me worry that I'll get pulled over again), but when I have high beams selected, all four lamps illuminate, so it's not the lamps or the sockets (I matched them to the old lamps, blew them out with compressed air and used electrical grease when I replaced them). So, they worked correctly once, but don't work correctly now.

2. Both the driver side and passenger side electric windows seem to start and stop working at random. Sometimes switching the plugs under the console will get one of them working, but I recently was stuck with both windows halfway down and neither one of them working, but they later started working again and I was able to raise them into their closed position. I've tried spraying WD-40 down the doors, thinking it might be age and lubrication, but that hasn't made much difference, plus I can't hear the window motor straining or working when they don't work, so appears to be electrical.

3. The radio (an aftermarket Pioneer CD-player), worked fine for weeks, then stopped getting power. I pulled it out of the console, verified that all the wires and plugs were seated properly, then pushed it back in to the console. Sometimes when I first start the car, the radio will power on, but later goes black all of a sudden. Sometimes when I'm passing Westport Connecticut (of all places), on the Merritt Parkway, the radio will come on again, then blink off. Unless the radio is haunted, I don't think that has anything to do with it.

4. When I looked under the hood (see attached), I noticed two wires ending in a small bolt that were just hanging free in the engine compartment. Should these be attached to something?

5. I also noticed under the hood a black wire behind the driver side headlight that is cut off, as well as 3 white plastic plugs, 1 of which isn't plugged into anything. Any idea what those were for?

I'd appreciate any thoughts or advice, and if you could manage to include a picture or two of what you're talking about, that would be fantastic.

Thanks,

Chris
 

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1986 560 SL
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7,358 Posts
The low beam lamps have two separate filaments, one lights for low beams and both for high. So you could have a burnt-out filament.
I believe the RH and LH low and high beams are all separately fused as well.
But the RH lows and the fogs are on the same fuse; if the fogs work the fuse must be good.
The rest of the gremlins beat me.
 

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1975 450SL
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The First things I would do would be to:

1). Twist the fuses in their holders, The stock aluminum fuses contacting the brass holder can create a non-conductive corrosion with time and moisture. The real fix is to get brass fuses and replace the aluminum.

2). Go through the cars' electrical system with a 1/4 inch drive set checking the tightness of the ground points. Also look for loose connectors and damaged wiring.

It does sound like a loose ground connection, somewhere.

Also, look at the battery terminals and connectors. If one of those is loose or corroded, it could give you these sort of problems.


Just tossing ideas out,
Scott
 

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chocolate brown 1974 Mercedes 450SL
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13 Posts
Discussion Starter #4
Thanks dugald and RadioTek! I'll try what you suggested and take it to my mechanic so that they can look at the grounding strap underneath the car, which was another possibility.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,362 Posts
When you get a minute fill in your profile with car and location.

If you are talking about the ground strap from the body to the engine it is attached to an upper transmission to engine bolt and into the body below the brake booster. It can be removed from the top.
 

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chocolate brown 1974 Mercedes 450SL
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Discussion Starter #6
In the end, I took it to my mechanic, who said the grounding strap was shot and replaced it. Everything has worked perfectly ever since. Living in a very busy part of Brooklyn, getting underneath the car wasn't an option, but thank you everyone for your suggestions!
 
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