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1983 Mercedes Benz 300D Turbo - Electrical Issues

01/08/2010 1:15 PM

I have a '83 300d turbo that has been having electrical issues recently. About a month ago I lost the function of the horn, and most recently both directions of the turning signals died. They worked in the morning, but not in the afternoon, and not since. I've checked the fuse box, and looked for a/the ground. I think/hope it's a ground issue, but I don't know. I also have no idea where to find the ground. Any help is greatly appreciated.

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#1

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/08/2010 11:19 PM

To figure if the trouble is a grounding issue use a jumper wire with probing points and with the key turned to on manually ground each item and see it they then work.

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#2

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 6:13 AM

A ground fault in direction indicators usually causes intermittent operation for a while before finally giving up. Where both stop at the same time, it is likely to be the flasher unit at fault - either feed, ground, or simply an old unit failing. Equally likely at the moment in the UK (much snow/cold) is old wires breaking due to corrosion - I needed to fully rewire an '84 Citroen CX due to this. Relays are often situated behind headlights, and older cars have primary fuseboxes under the bonnet (hood) which tend to decay with age. As for earth points, there is usually a main one on the inner wing near the battery, but also near to each device within the car - so one will be hidden somewhere behind the dashboard, usually near the centre for cars which are made in left- and right-hand versions (behind radio is a favourite). Flasher units are mostly on the main fuse board for later cars, but on the column for earlier ones. (change came in the 80's)

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#3

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 7:40 AM

Buy the car manual with circuit diagram.....

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#4
In reply to #3

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 9:44 AM

Thanks, I plan on doing that today. There are some other issues with the car, and the manual would be the best place to start.

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#5
In reply to #4

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 4:21 PM

Definitely get the manual, and get one in which the wire color code is shown. (VW used to [and may still] actually print the schematic in the wire colors, so you didn't have to squint to read the color codes. Merc may do the same.) But in any case, being able to trace the wiring is essential. Then, any troubleshooting is very straightforward: you can either start at the source and work toward the powered device, or vice versa.

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#6
In reply to #5

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 9:51 PM

A long time ago I was taught to start in the middle of testing an electrical circuit, not at either end, therefore elimanting 1/2 of the circuit with the first test.

Of course test at the easier access points.

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#7
In reply to #6

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/09/2010 10:20 PM

You're right. Oddly enough, I even taught that method (remotely) to some industrial electrical types (via a CBT course I developed, that had a troubleshooting simulator built in). We called it the half-split method. But in practice, I don't use it (unless coincidentally) on cars. Access is a key issue, circuit simplicity is another (it's rare that you can't find a problem very quickly in a car) and just gut feel being another. In lighting circuits, the problem is usually the bulb or its socket, so if you start there you are likely to spend less time than if you try to gain access to switch terminals.

But your point is entirely correct. It's interesting to have the memories triggered -- I haven't thought about the method or the course for years... decades!

... again thinking back, we used to ask people to guess any number between 0 and 100 in seven guesses, which you can always do with the half-split method.

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#10
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Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/10/2010 8:49 PM

Thanks for the reply. I did not think "off topic" but apparently 5 people did? possibly because it didn't talk about a Mercedes.

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#11
In reply to #10

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/11/2010 12:01 AM

If you vote your own post "off-topic" (which I did) you get an automatic 5 votes -- which I think may the be the threshold for having it minimized (if minimization is set as your preference). I thought my post probably would not help with the Mercedes owner's problem -- it's more along the lines of reminiscing.

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#12
In reply to #10

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/11/2010 5:03 AM

You probably marked yourself off topic by replying to an off topic post.

This makes you automatically 5 votes off topic, just like this post will be!!!

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#8
In reply to #5

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/10/2010 4:45 AM

I hope that its color coded too, but for a car of this age I feel it may not be, sadly.....

But I'll keep my fingers crossed for luck in that direction!!

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#9
In reply to #8

Re: 1983 Mercedes Benz 300D Turbo - Electrical Issues

01/10/2010 10:47 AM

At that age they're likely to be better - if not fully colour coded, you get individual wires shown. Whereas now the books are written by harness: wire4 from here disappears into this harness.........no indication where it goes from there!

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