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  #1  
Old 04-11-2005, 09:45 PM
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Question shorting battery?

Ok fellas, I have really enjoyed reading all your posts and your comments have been extremely helpful. Now to the electrical mystery on my 300SD 81'. Something is either draining or shorting my 3 month old battery while I drive, the motor runs fine until turned off. (a testament to MBz toughness) I checked the following
1. Fuse drain, with fully charged battery seems O.K.
2. Alternator (newer) and regulator (brand new) tested fine
3. Battery tested for internal shorts seems O.K.
4. New belts on alt. and ajusted them twice to less freeplay
5. Ground cleaned and reattached and motor to chassis ground is fine
Could the starter soleniod or relay be doing the damage?
I really appreciate all ya'lls help and expertise


Last edited by BigBenzno; 04-11-2005 at 09:53 PM. Reason: forgot to add new regulator
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  #2  
Old 04-11-2005, 09:59 PM
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Possible:

Glow plug relay stuck on = dead battery while driving.
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  #3  
Old 04-11-2005, 10:16 PM
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Quote:
Originally Posted by BigBenzno
Something is either draining or shorting my 3 month old battery while I drive, the motor runs fine until turned off.
Welcome to the forum.

Please explain in more detail. Describe the symptoms of the problem rather than your interpretation of them.
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  #4  
Old 04-11-2005, 10:25 PM
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Is there only a draw while the key is on?

The glow plugs draw 50-80 amps, more than your 55A alternator can pull to keep up.
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  #5  
Old 04-12-2005, 06:57 PM
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Thank you for replying, the car runs fine then twenty minutes later while cruising on the the freeway the electrical cuts out everything except the motor...Also used the multimeter to test the resistance on the GP relay and nothing comes up, tried to test the amps at the battery while the car was on and the multimeter started to fry? weird...I guess its driver error any way thanks for your help I want to keep her as long as I can.
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  #6  
Old 04-12-2005, 07:03 PM
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82-300td the ignition is on when i tested for amps and it fried the mmeter, whunter I will try to replace the relay and I'll let ya'll know what happens once again THXs
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  #7  
Old 04-12-2005, 07:03 PM
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Most of the meters offered to us will only handle 10Amps!

......
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  #8  
Old 04-12-2005, 08:18 PM
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Quote:
Originally Posted by BigBenzno
Thank you for replying, the car runs fine then twenty minutes later while cruising on the the freeway the electrical cuts out everything except the motor...Also used the multimeter to test the resistance on the GP relay and nothing comes up, tried to test the amps at the battery while the car was on and the multimeter started to fry? weird...I guess its driver error any way thanks for your help I want to keep her as long as I can.
When you start the vehicle in the morning, test the voltage at the battery with the engine speed at about 2000 rpm. See what it reads.

Then, when you are driving and the problem shows up, pull over to a safe place and, again, with the engine speed at about 2000 rpm test the voltage at the battery.

Report back with your results.
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Old 04-12-2005, 09:29 PM
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The battery will run the car but if you drive it enough the level will be 9V or lower almost completly dead the next day its totally gone 0V on meter. I can jump start it but it never powers up i.e. no electrics on car, but it will start with a jump. Contacted local MBz dealer for the GP relay and I'll try that this weekend. Left the (+) disconnected so it won't drain my recharged battery THX
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  #10  
Old 04-12-2005, 09:42 PM
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Quote:
Originally Posted by BigBenzno
tried to test the amps at the battery while the car was on and the multimeter started to fry? weird...I guess its driver error
This won't fix your car, and I don't want to derail the thread too badly, but...

... exactly how did you hook up your multimeter to "test the amps at the battery"?
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  #11  
Old 04-12-2005, 11:06 PM
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Quote:
Originally Posted by BigBenzno
The battery will run the car but if you drive it enough the level will be 9V or lower almost completly dead the next day its totally gone 0V on meter. I can jump start it but it never powers up i.e. no electrics on car, but it will start with a jump. Contacted local MBz dealer for the GP relay and I'll try that this weekend. Left the (+) disconnected so it won't drain my recharged battery THX
The first issue is to determine why you have no output from the alternator. If you jump start the vehicle and nothing else in the vehicle works, then the alternator is not working. You have either a bad regulator or a bad alternator.

This must be corrected prior to doing anything with a glow plug relay. It's highly unlikely that the relay is remaining closed and causing this issue.
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  #12  
Old 04-13-2005, 07:34 PM
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I too thought it was a bad alternator and removed it to have it tested 'round the corner at NAPA and everything tested O.K. on their new computer thats whats confusing me. I can run the car with no (neg.) cable hooked up but there is no electrics on the car... touched the pos. to terminal and the neg. to ground... did I mess that up too?
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  #13  
Old 04-13-2005, 07:53 PM
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OK, if NAPA tested the alternator and it is OK, please go back and perform the procedures that I outlined in post #8.

Something strange is going on here.
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  #14  
Old 04-13-2005, 08:10 PM
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Do you see why its such a mystery to me? it will run just fine until the battery looses its juice and it never gains it back, double checked the regulator and the brushes seem new and shiney. So I tried your test and once the battery dies thats it. I have all the reciepts from the PO and the regulator was bought in Jan. A comment on the reciepts says repaired electrical drain but I followed some steps from other threads here and nothing seems to be draining
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  #15  
Old 04-13-2005, 08:14 PM
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Quote:
Originally Posted by BigBenzno
So I tried your test and once the battery dies thats it.
Please explain in more detail.

My test involved the use of a voltmeter when you start the engine for the first time in the morning and when you notice you have the problem.

Additionally, the suggestion of Mr. Hunter should now be investigated.

After the engine is running, attach the voltmeter to one of the glow plugs and see if there is any voltage at the glow plug after the engine starts.

The voltmeter will be the tool to find the problem, if you use it exactly as I have explained to you.

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