wiring diagram for voltage regulator/alternator on 300D? - Mercedes-Benz Forum
 
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#1 (permalink) Old 02-18-2010, 03:14 PM
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wiring diagram for voltage regulator/alternator on 300D?

I'm blowing voltage regulators left and right at the moment(possibly due to my blower motor) and I'm trying to look into how I might build a better one that on this cheap replacement that I've been given. I'm seriously considering using like an old Mopar external regulator and just wiring it to the regulator that's in it now.

Anyone got a rough diagram of how the alternator/regulator wiring works?

I promise to share my ideas once I have a functioning system.

Thanks

Eric

1983 300D turbo
1969 280SE
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#2 (permalink) Old 02-20-2010, 11:47 PM
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It would be helpful if you could give more info like the charging Voltage you are getting and at what speeds you are getting it at and what happens to the Voltage when you turn your Lights and accessories on.

In 2 years of reading on Forums I have not read of the Blower Motor causing blown Voltage Regulators.
But, you could remove the Blower Fuse and see if your problem goes away. That would prove the Blower is the cause of the problem.

I would be looking for a bad Ground (the V Regulator in this case controls the current to the Fields by grounding the regulator) or bad conections between the Battery and the Alternator.

There is a metal part of the Voltage Regulator (at one of the Retaining Screw holes) that contacts the Housing of the Alternator. If the Alternator Housing in that area is not making a good contact it will not ground well.
The Engine to Chassie Ground Strap could be unbolted and the contact area cleaned up so it makes good contact as well as where the Battery Ground Cable attaches to the body the Body.

Next, the Connector/Plug can also have poor conduction issues due to Oil, dirt, or oxidation.

On the Connector the 2 large slots with 2 fat Red wires should be getting Battery Voltage all of the time. One of the Wires goes to the Starter where the + Battery Cable attaches to the Starter.
I believe the other goes to the Terminal Block in front of the Battery (US models).
The smaller slot with the skinny Blue wire should get slighly less than Batter Voltage; but only when the Ignition Key is on. This is the circuit that goes to the Dash No Charging Warning Lignt.
The Bulb for the warning light is suppsed to be 3 watts or your Alternator will not charge.

Last edited by 300Dman; 02-20-2010 at 11:56 PM.
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#3 (permalink) Old 02-23-2010, 03:15 PM
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Quote:
Originally Posted by 300Dman View Post
In 2 years of reading on Forums I have not read of the Blower Motor causing blown Voltage Regulators.
But, you could remove the Blower Fuse and see if your problem goes away. That would prove the Blower is the cause of the problem.
Have you ever seen a blower motor blow a fuse? If they can do that, they can overload a regulator. Mine had been blowing 25 amp fuses every now and then so I'm pretty sure it's a good indication that the blower is a contributor. I've been working on cars(not just reading forums) since the mid-to-late 80's and have seen this(overloading the alternator/regulator) happen lots of times.

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