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  #16  
Old 12-19-2006, 11:45 AM
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Quote:
Originally Posted by 240Dog View Post
Am honestly beginning to believe Mercedes Benz has the crummiest electrics of any car built.
It is obvious you have never owned a Jag......

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  #17  
Old 12-19-2006, 12:24 PM
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Quote:
Originally Posted by JimmyL View Post
It is obvious you have never owned a Jag......
As the former owner of a 1957 XK 140 fixed head coupe...and three 6 cylinder MGC's ... All LUCAS electrics from England I must concur with Jimmy's evaluation of the situation.
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  #18  
Old 12-19-2006, 12:30 PM
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I just looked in the Haynes manual wiring diagrams...
it shows in the instrument cluster attached to the ' charge indicator light' a diode and maybe a capacitor ... too small to see ....
And it shows 9 diodes at the alternator... I suspect 6 in the alternator and 3 in the regulator section...
So what I am saying the long way is that the soft glow /increasing in brightness is typical of an electrical switch operating it...as compared to ON/OFF.... and that they can degrade over time... your charging system may be off.... but it may just be that your indicator circuit is old and giving you bad indications... so don't spend too much money fixing one without checking out the other first...
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  #19  
Old 02-04-2007, 12:30 AM
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gimme a low-tech 240D
 
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Okay, its been awhile and I've been driving my parts car most of the time - but here's what I'm finding out....... PO left a rat's nest in the under-dash wiring. Beaucoup hot leads running dead ended, spliced into socket connections too. Looks like he tried to hook-up an idiot stereo system using trial and error. Then he pulled the stereo selling the car. For all i know, his reason for selling was the electric probs.

Have retaped a few wires stripped of their insulation that I've found, also ripped out alot of the junk he left dangling - and the situation has IMPROVED! Now the alt light comes on less frequently at high rpm's.

Quote:
chopped up wiring near the radio should not cause charging problems
Not true, says me. Am now believing that fluctuating electrical load that feedbacks to the alternator is directly related to wires being crossed, also mixed up and left dangling.

Meanwhile if anybody mentions the fanbelt again then I'll slug em. And the car has a history of eating alternators according to service records. The one in there now is less than 3 months old, installed by me.

Quote:
Zener diode to use up the excess electricity made by the generator....
That might be a quick fix for me that I'm lookin into. Spoke with radio shack about it and they said it must be matched to amp loads.
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  #20  
Old 02-04-2007, 01:21 AM
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240Dog,

The alternator does not make excess electricity if the voltage regulator is working correctly. The regulator keeps the voltage output of the alternator at about 14.5 volts which is the correct voltage to properly charge the battery. When the battery is fully charged, the voltage of the battery equals the voltage of the alternator and current stops flowing into the battery.

Other electrilcal consumers in the car draw current proportional to their resistance up to the capacity of the alternator in amperes. Thus an alternator is rated by the amount of current in amperes it can generate I.E. a 55 amp alternator.

There have been voltage regulator systems made that use a Zener diode to regulate the voltage, but these systems are inefficient because they have to dissipate energy in a resistor. They are usually used in a very low current circuits. The voltage regulator in a MB system controls the field current of the alternator to regulate the output voltage and needs no Zener diode in the circuit.

P E H
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  #21  
Old 02-04-2007, 01:32 AM
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Alt Lamp

Sounds like the Alt is churning out all it can to supply the mystery load....
A very good test would be to actually measure the current output of the Alt. in the car at different speeds to determine if the Alt is having to put out more than is normally required with normal system draw...

Eating Alternators is an indication of constantly running near the max output...which will certainly shorten service life....and could be the cause of the lamp as the alt struggles to keep up..........That is why the alt. current output test is so important....

Sounds like you are on the right track...get rid of the extra wiring and reconfigure as close to normal as you can....I think you are close to finding the mystery load on the system...
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  #22  
Old 02-04-2007, 08:28 AM
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gimme a low-tech 240D
 
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Quote:
Originally Posted by P.E.Haiges View Post
240Dog,

Other electrilcal consumers in the car draw current proportional to their resistance up to the capacity of the alternator in amperes. Thus an alternator is rated by the amount of current in amperes it can generate I.E. a 55 amp alternator.
Okay, then it sounds like what I've got is arcing occurring somewhere proportionate to engine speed or alternator output. Like something is pigging the amps or resistances are all screwed up?

Another scheme of mine to help find the messed up circuit is to pull the fuses individually to see which branch of the tree it might be. Otherwise all the electric appliances are operable, well except the electric antenna.

Looks like really sloppy work had been done with an exacto knife on the wiring harnesses under there. Have also found dead-end leads under the carpeting and improvised junk in the console around the forward/rear radio speaker dial. Meanwhile none of the service records indicate that any professional radio installer has worked on the car.

Quote:
..get rid of the extra wiring and reconfigure as close to normal as you can...
Good advice, thats what I'll be tryin to do. Seem to be having a little success already as the alt light has quieted down a bit.
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  #23  
Old 02-04-2007, 10:49 AM
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240Dog,

It the alternator was putting out a full 55 amps or so, that would be over 600 watts and there would be a very hot spot where the almost short circuit was and in the wires going to it. So look for any hot spots.

Its probably not in a fused circuit or the fuse would blow out. Almost any wires except ones in the GP and starter circuit would get hot enough to smoke with that much current going thru them.

I agree that it would be a good idea to measure the output current of the alternator.

P E H
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  #24  
Old 02-04-2007, 11:28 AM
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im not sure if you stated the unloaded output of your alt. was low. if it was low this link might be worth lookin at.
http://www.dieselgiant.com/mercedesvoltageregulatorinstall.htm
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  #25  
Old 02-04-2007, 03:43 PM
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Messed up wiring on 240D

If you need to know where some of the wires go...or if any unidentified wires belong there or not....I have the carpets, glove compartment, instrument panel and knee bolsters out of my 1980 240D....Just let me know which colors or locations that are in question and I can dig them out....kevin
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  #26  
Old 02-04-2007, 05:24 PM
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Check DC voltage at the battery and also check AC voltage at the battery. If the AC voltage is very high (search for the numbers) one of the internal diodes in the alt is bad and is destroying the battery with AC voltage.
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  #27  
Old 02-04-2007, 06:43 PM
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Car going through a lot of alternators is usually bad quality replacement units or staying with a bad battery. Because of say a dead cell the alternator never gets a rest from charging. It's just trying to catch up but it just can never get there.
To get a grip on your situation I would wire a voltmeter into say the cigarette lighter socket. Watching what your meter does voltage wise over a couple of days is going to lead to some conclusions pretty fast I think. Or at least indicate where you have to look. There is something strange here.
If you can make that light glow with manipulation of the throttle while car is stationary just monitor the battery voltage. If it is say 13.5 volt for example. Rev the engine a little and watch your voltage. If it rises a little that is normal.
You will have to have a second person to inform you of any indicator light change. If the voltage also declines a little that is also meaningful. The problem with a leaky diode concept is usually the leakage would be constant. It possibly could be intermittent but not likely. This methology will start to zero you in on exactly where or what the actual problem is.
There is a good chance for example that the alternator is putting out properly yet the indicator circuit is intermitently malfunctioning. Prove that first. Could also be the alternator is not producing consistantly as well. Voltage monitoring should help a lot. Your suspicion that something is wrong in the wiring could be valid. I just had a look at a wiring diagram. I was not estatic by what I saw. But first eliminate the other possibilities. The indicator circuit does look a little more complex than what I thought it should.

Last edited by barry123400; 02-04-2007 at 06:48 PM.
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  #28  
Old 02-05-2007, 07:40 AM
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My alternator behaved a bit like described. It was a bad alternator - I think the voltage regulator was blown. Replaced it and my voltage sits at 13.7v, 13.3 with the lights on.

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