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i Have an 83 300SD that i recently purchased and have been using as my daily driver, everything worked fine at time of purchase but things have been slowly going down hill. Until recently the car had to electrical issues other than the intermittent blower motor.

Well last night we were taking a 100 mile trip for a family emergency and the car begin to act up, half way there the seatbelt light kept coming on and going off and when anyone hit any switches the lights would dim or the buzzer would go off. It was obvious there was some kind of short somewhere. Well when we pulled over to take a rest stop and when we went to turn the car on we had a total loss of power, not a single light would turn on, it seemed as if the car had completely died, it was unresponsive to everything. :confused:

We attempted to jump it thinking it was the battery but still had no response. I checked all the fuses and looked for any apparent damage and could not find anything. Not a single fuse had blown. After getting the car home today, I did a more thorough investigation an still found nothing, the main ground had the plastic on work through but when I checked power from battery to block and battery to frame on the voltemeter it still read 12.64. I have no idea what the problem could be and have begun to comb through all the wiring in the car....

please help any information would be greatly appreciated. :thumbsup:
 

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Check your alternator. A bad one can burn up a good battery ASAP and when the alternator is wonky it'll do lots of strange things.
 

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Hello Freind,
I am a new member here, and am feeling your frusturation. I am not too mechanically inclined, but I advise you to take the car to your local quality mom and pop interior/electrical shop, someone you can trust. It sounds like this problem is effecting multiple interior locations, meaning it is being caused by the "managing system/unit" if you will. Best of luck, and I hope everything works/ed out with your family emergency.
Regards,
Der Bomber:thumbsup:
 

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So i attempted to by pas the starter solenoid and had not luck I also checked all the leads going to the alternator and they are all good and carry current, I am at a complete loss here. Does anyone have a wiring diagram for a W126 300SD.

And is it possible for the battery to still have voltage but be completely dead.. I also attempted to test the voltage at the junction in the fuse box and could not get a reading, could my positive wire have been severed somewhere

once again any information would be greatly appreciated.
 

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Your battery can have a bad cell and still have voltage, but when you try to start the car the battery hasn't enough reserve to overcome the draw on the battery. Have you tried to Jump the battery to start the car, then check the alternator to see if it is working well. It should put out 14 volts or there about if good.

Your started can be bad also and if so it puts a lot more draw to start as well.
 

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Well last night we were taking a 100 mile trip for a family emergency and the car begin to act up, half way there the seatbelt light kept coming on and going off and when anyone hit any switches the lights would dim or the buzzer would go off. It was obvious there was some kind of short somewhere. Well when we pulled over to take a rest stop and when we went to turn the car on we had a total loss of power, not a single light would turn on, it seemed as if the car had completely died, it was unresponsive to everything. :confused:
Sounds to me like the voltage regulator. About $30 part and easy to replace. Much cheaper than replacing the alternator. I'd start there.

Also, be sure you have upgraded all the fuses to copper. If the metal on the fuses is silver colored, replace them with new copper ones and clean the contacts well. That will eliminate many electrical demons. I'm 99% sure this isn't your main problem (I'd put money on the voltage regulator) - but worth checking out.
 

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i Have an 83 300SD that i recently purchased and have been using as my daily driver, everything worked fine at time of purchase but things have been slowly going down hill. Until recently the car had to electrical issues other than the intermittent blower motor.

Well last night we were taking a 100 mile trip for a family emergency and the car begin to act up, half way there the seatbelt light kept coming on and going off and when anyone hit any switches the lights would dim or the buzzer would go off. It was obvious there was some kind of short somewhere. Well when we pulled over to take a rest stop and when we went to turn the car on we had a total loss of power, not a single light would turn on, it seemed as if the car had completely died, it was unresponsive to everything. :confused:

We attempted to jump it thinking it was the battery but still had no response. I checked all the fuses and looked for any apparent damage and could not find anything. Not a single fuse had blown. After getting the car home today, I did a more thorough investigation an still found nothing, the main ground had the plastic on work through but when I checked power from battery to block and battery to frame on the voltemeter it still read 12.64. I have no idea what the problem could be and have begun to comb through all the wiring in the car....

please help any information would be greatly appreciated. :thumbsup:
Do following and let us know what happened.

1- Remove negative terminal from the battery. Check the voltage at the battery. It should be around 12.6 volts.
2- Connect negative terminal of the jumper cable to the negatve battery terminal and other end of the negative terminal of the jumper cable to the engine block. Make sure the wiring connection to the starter is tight.
3- Try to start the car. If car starts, replace the negative cable from battery to the engine block.
4- Make sure the positive terminal of the battery is also clean and tight.

You car should start if starter is good. Otherwise remove the starter and bench test the starter directly from the good battery.

Let me know what happened.


Sahai
 
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