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post #1 of 6 (permalink) Old 09-30-2010, 03:09 PM Thread Starter
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Date registered: Sep 2010
Vehicle: 72 250c
Location: Near Calgary, AB
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(Thread Starter)
First Mercedes, electrical trouble.

First off, hello out there! I've been visiting this site for the past month and have found it to be a great source of information, however a problem has been confounding me with a 72 250c. Its in a fairly bad state of repair, but due to it being a gift. I've been slowly trying to get it running. The engine cranks perfectly fine, but there is no spark.

In trying to repair the problem, I've replaced a cracked distributor cap, adjusted some wiring, timed the spark wires, replacing them with new wires. There was two coils in the vehicle at the time of purchase, and I have installed one of the coils that seems fine in my tests. I have also replaced all the fuses, which also lead to the same result.

I do not trust the wiring job that is currently in place, but having no electrical diagrams has been a problem. The lighting is perfectly fine, and when the car is turned over, the lights dim, making me assume it isn't a problem with the ignition switch.

I'd be a great help for any advice on the situation, I can provide pictures of whatever is required. I really hope to get this 250c back on the road. It doesn't deserve to keep rusting away in a field.
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post #2 of 6 (permalink) Old 09-30-2010, 05:52 PM
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Date registered: Apr 2007
Vehicle: 1999 E320, 1975 450SEL, 1979 280SE
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Do you have a voltage tester or test light? Use a tester or meter to make sure that you are getting voltage to the coil. There are ways to jump a wire to the coil from the battery to see if the engine will start. As long as the points and condenser are good, the plugs should spark. There are plenty of web sites that can provide a wiring diagram, also. Good Luck! Let us know how it goes.
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post #3 of 6 (permalink) Old 09-30-2010, 06:16 PM
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Date registered: Jun 2010
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To rabbit188 - what are the websites that offer wiring diagrams. I also have a 72 250 with AC electrical problems. A wiring diagram would be very helpful. Thanks.
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post #4 of 6 (permalink) Old 10-01-2010, 04:56 AM
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Date registered: May 2007
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Dimming lights while cranking is an indicator of a weak battery thus no volts for the sparking.

Brian O
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post #5 of 6 (permalink) Old 10-01-2010, 01:29 PM
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Just for test purposes wire the coil directly to the battery bypassing all wiring in the car. This should quickly tell you if it is a wiring problem. Don't leave the coil connected for more than a minute or it may damage your coil because you are bypassing the ballast resistors and the points may be closed allowing current through the coil.
this is known as "hot wiring" a car.

Tony
280SE 3.5 Coupe
Stick shift
3.27 Axle
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post #6 of 6 (permalink) Old 10-01-2010, 04:43 PM
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Quote:
Originally Posted by Miss Daisy View Post
To rabbit188 - what are the websites that offer wiring diagrams. I also have a 72 250 with AC electrical problems. A wiring diagram would be very helpful. Thanks.
You can do a search for "free Mercedes wiring diagrams" or "free Mercedes wiring schematics". Some sites are: Free Ebook, Wiring Diagram Ebook, Service Manual Ebook, Electronic Circuits, Automotive Ebook, more Free eBook Download and Free Auto Repair Question Online Mechanics Answer Questions FREE. Also, a really good site for manuals at a good price is: Mercedes Benz Manual - Mercedes Repair Manuals - Mercedes-Benz Service Manuels.

I have a wiring diagram for the 250C that I could scan and email to you. But, it does not have A/C on it. Back then, most A/C units were added by dealers, using Thermo-King units. Thus, the A/C is not shown on the factory wiring diagram. You may have luck with searching Thermo-King or Behr, depending on which unit you have. Hope this helps!
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