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  #1  
Old 12-15-2011, 07:20 PM
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1982 300td battery light on

My battery light is staying on. It glows dimmly then gets brighter on acceleration. I checked the voltage at the battery and it is 13 and goes up to 14.8 when I rev the engine high. I changed the voltage regulator and it is still the same problem. What should I check next?
Thanks in advance for the help.
Liz in Los Angeles

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Old 12-15-2011, 07:40 PM
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There is a small blue wire attached to the alternator next to the larger power wires. See if you can measure the voltage on this wire with the engine running............
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Old 12-15-2011, 08:02 PM
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Quote:
Originally Posted by Brian Carlton View Post
There is a small blue wire attached to the alternator next to the larger power wires. See if you can measure the voltage on this wire with the engine running............
Is that running with the Connector disconnected from the Alternator or running and you tap into the Blue Wire? (The Blue Wire connects to the Charging Light.)
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Old 12-15-2011, 08:09 PM
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13 Volts is too low in one of the Manuals it has 13.3 as the lowest acceptable Voltage; 13.5-14.5 is Batter.
Slipping Belts/worn Pulleys?

The Alternator needs a good ground to function properly.

This also means that the one of the 2 screw holes on the Voltager Regulator has a ground tab on it. If your Alternatorl Frame is old and oxidized it may not ground well.

Another thing people have done is to connect 1 Jumper Cable to the Negative Terminal of thel Battery and apply it to the Frame of the Alternator. If the Voltagle goes up you have a ground issue.

You might remove the Alternator and have it tested for free. I do not know what speed they test at but if they can duplicate an Idle speed that the Alternator would turn and your Alternator Is OK it could indicate you have a wiring issue. The Connector itself often gets corroded.
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Last edited by vstech; 12-16-2011 at 03:07 PM.
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Old 12-15-2011, 08:13 PM
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Originally Posted by Diesel911 View Post
Is that running with the Connector disconnected from the Alternator or running and you tap into the Blue Wire? (The Blue Wire connects to the Charging Light.)
You need to do it running...........want to see if there is 12V going to the light.
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Old 12-15-2011, 08:45 PM
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I think the voltage started over 13. I was worried I am overcharging battery. The new voltage regulator said 14.8v on the side of the box. Isnt a reading of 14.8 overcharging the battery? Its dark out now so I cant check the blue wire. Is it on the connector that clips into the side of the alternator? Should I undo the connector and check the voltage? I read somthing about that on another post. It seems to me that the light would go bright when the battery was not charging, but it gets brighter when I excelerate. When I check voltage at the battery it is higher when engine reved. I dont want to toast my battery and get stranded somewhere.
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Old 12-15-2011, 09:11 PM
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14.8? The MB regulators Ive seen are 14.1. What was your source?

Low voltage on these cars is common. High to me is rare. Id get your alternator checked to see if there is some aspect of the protective devices and whatnot that is creeping it up. 14.8 is a bit high to me, though 14.3 would be nice.
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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
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  #8  
Old 12-15-2011, 10:05 PM
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Originally Posted by kdvrwgn View Post
I Its dark out now so I cant check the blue wire. Is it on the connector that clips into the side of the alternator? Should I undo the connector and check the voltage? .
Yes, it is on the connector.

No, you cannot undo the connector............you must check for voltage with the connector attached and the engine running.

Be careful..........it's not in a safe place relative to the fan.
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Old 12-15-2011, 10:07 PM
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Quote:
Originally Posted by JHZR2 View Post
14.8? The MB regulators Ive seen are 14.1. What was your source?

Low voltage on these cars is common. High to me is rare. Id get your alternator checked to see if there is some aspect of the protective devices and whatnot that is creeping it up. 14.8 is a bit high to me, though 14.3 would be nice.
With nothing electrical on I get a raging 13.7 Volts at idle.
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Old 12-15-2011, 10:44 PM
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Sounds scary. I have a voltmeter but not sure how to check. Can you please explain? The wire is insolated right?
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Old 12-15-2011, 11:13 PM
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Sounds scary.
I would therefore advise against making this test if you are not confident of how to do it safely.
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Old 12-15-2011, 11:17 PM
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How do you test an insolated wire? remove some of thr insolation and touch it with the probe from the meter?
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Old 12-15-2011, 11:18 PM
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Quote:
Originally Posted by JHZR2 View Post
14.8? The MB regulators Ive seen are 14.1. What was your source?

Low voltage on these cars is common. High to me is rare.
I have had 17 volts at idle in my 420sel once! I noticed my dash lights were super bright.

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