1977 Mercedes 280E not charging - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 05-26-2006, 10:03 PM Thread Starter
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Unhappy 1977 Mercedes 280E not charging

I bought a 1977 Mercedes 280E a few months ago. It has a charging issue. Looking over the paperwork it has had this problem for years, and the previous owner had spent $1700 trying to fix it to no avail. (likely one of the reasons he sold it, (I have had to repair many items)) It has a new alternator, starter, and battery. It has had these items replaced several times with no change in charging voltage.

This is what is happening: Start the car and charging voltage reads about 12.1 volts. Readings the same at battery, and at back of alternator. Start turning accesories on and it continually goes down to as low as 11.2volts. With absolutely no accesories on it will eventually charge up to 12.6 volts. As I watch the voltmeter it will occasionaly(once every 10 minutes for 2 or 3 seconds) jump up to 13.5 - 14.2 volts and stay there very briefly. There was absolutely no corrosion anywhere, but I still cleaned all connections with sandpaper, no change. I ohmed out the alternator charging wires and they are good. The warning light is functioning properly, and lights when alternator is disconected and lead is grounded. I pulled every fuse and ran the car, no change.The vehicle has zero amp draw with the clock disconnected, so no shorts present I am totally at a loss here, after 4 alternators I know that cannot be the problem.Anyone have any ideas?

One more thing, there is a junction block where the wires from the alternator meet. It has three posts, one connects the alternator charging wires to a wire that goes to the starter.One connects to the starter solenoid and the ignition. The other one is in the middle and has a pink wire coming from the wiring harness , and one going towards the starter. The pink wire reads about 9.8 volts when the battery reads 12.1, the wire going towards the starter never reads any voltage. Does anyone know where these wires go, and if the voltage should be higher?Or does anyone have a wiring diagram to help me find out?
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post #2 of 4 (permalink) Old 05-27-2006, 02:24 PM
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Any other electrical problems, however small?

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post #3 of 4 (permalink) Old 05-27-2006, 03:05 PM Thread Starter
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The only thing I could consider an electrical problem, is occasionaly while driving if you turn on an accesory the seat belt warning light comes on for a second. It also comes on once in awhile just driving around.
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post #4 of 4 (permalink) Old 05-27-2006, 04:08 PM Thread Starter
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update: the middle wire(red with purple stripe 14gauge) of the junction block that is reading low voltage is reading 1.8 on my ohm meter. I dont have a wiring diagram so I am going to try and trace it through the car and see where it goes, and if it goes to a faulty component or has a short.
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