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Discussion Starter #1
I have been trying to solve a battery/charging problem for the past 3 months, and I'm about well fed up with it.

Battery is brand new and holds a charge just fine. I've had it tested multiple times. The alternator has been swapped out 3 times now, and none of which seem to be doing the job. I tested the first 2 (one of which being the original) and they were bad. I have not tested the new one, only because the local Auto Zone refuses to test it.

Just as a side note, I am also having a problem with the number 2 fuse. It pops whenever I try to put in a new one. I went to check the wires, and at a first glance they seem alright.

My guess is that the battery is getting a drain due to the number 2 fuse, but thats only a thought. Anyone have any other ideas?
 

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1985 380SE
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Test your voltage regulator in addition to the fuse as Govert70227 said. it's on the back side of the alternator.
 

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Discussion Starter #4
Fuse 2: Clock, trunk light, diagnostic, roof light front + rear, hazard warning system, illuminated vanity mirror, warning monitor term. 5, autom. antenna, switch-over valve seat back arrester, (electronic radio).

How do I test the voltage regulator in the Alternator?
 

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1984 300D
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You never answered if your Battery (no charging) Lignt goes on when you first rotate your Ignition Key (actuall all of your warning lights should go on when you firt turn the key, this is to check if the Bulbs are working)?

If the Bulb is burned out your Alternator will not charge bacause the way it is set-up up you need the resistance of that Light Bulb in order for the Alternator to charge.

Just put your Volt/Ohm Meter (multimeter) arcrossed the Battery Terminals and report the Voltage you are getting when the Engine is runing.

If the Alternator is still off take it to another Autozone you have never been to; or, to another Auto Part store that does free testing.
Better to test the Alternator with it off of the car. If it passes the test you could be haveing a problem with the wire connections. Those could be anything from the Plug that goes into the Alternator Voltage Regulator to the Ground Straps on the Engine. If any of them are not making good contact they can cause problems with charging.

On mine the Engine to Chassis Ground Strap is about where your Feet are when you sit in the Drivers seat; but, under the Car.
 

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Discussion Starter #6
Right now my battery is very low, so the Voltage on it will be reported as very low.

We fitted the new Alternator on last night, and the battery was at 12.6v when I left the garage ~ 30mins of driving at highway speeds + head lights and radio, battery was showing ~10v charging from the alternator.

Dashboard is all messed up. After a clutch install, the temperature and fuel gage hasn't worked since. The seatbelt light is always on, and the battery light is always on.
 

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1984 300D
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Release the wire spring and pull off the Wire connector at the Glow Plug Wire.
There is 3 wires attached to the Connector. The 2 long Connector Slots are connected to 2 Fat red Wires. Both of those wires are connected to the Battery and should have the same Voltage as the Battery.
The 1 small Connector Slot is connected to a skinny Blue wire. That is the wire that goes to the Battery No Charging Warning Light.

With the Key off there should be no Voltage there at all.

With the Key in the start or run position you should get slighty less than the Battery Voltage there.
If when the Key is on you are not getting Voltage there you have an open circuit. This could be caused by a burnt Bulb in the warning light or a problem with the Ignition Switch.
I do not know if a problem with the Ground in your Gauge Cluster could cause that or not.
 

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Discussion Starter #10
Massive update.

After cleaning the two 12v rails to the alternator, the system starts to charge once again. I soon realize after that the car was not charging enough and when using everything plus brights, the system would not charge at all. However, the car still lasted for an entire week at roughly 12.4v and had no problems starting or running. I just could not use the brights.

Today I drove to my friends place, (5min ride), was only there for about 10mins, came back out to go home, and the car was dead. We popped started it and took a look at everything. Everything was fine, in fact, everything was better. Instead of getting a lousy 12.4v RUNNING voltage, I was now at 13.5v RUNNING voltage. We put a scope up to the line to see amperage draw, and everything was fine.

We then turned the car off and than back on and saw that it now went back to its usual state: 12.4v Running Voltage. But soon after it kicked back in. My friend jiggled the battery grounding voltage line and it popped back up. But we could never simulate that same situation. We tried a couple times to see if the car would go back to its normal 12.4v Running voltage but couldn't.

With all the information from this post, and from above, is there any clues you guys could give me that may cause something like this? Could it be any of the 12v regulators in my car or on the Alternator?

Just as a reminder, I still have the number 2 fuse broken, so something is draining but its intermittent.
 

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1985 500SEC; 1984 300TD; 1984 300CD; 1985 300CD; 1978 280CE
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What about the connection between the battery ground cable and the chassis? I had a similar problem (except the fuse) and fixed it by cleaning that with a wire brush.
 

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Discussion Starter #12
Well the logical answer is this, if I wasn't getting a clean connection to from the battery ground, than I would have a charge on the system at all. A complete connection would not be possible. At least thats how I see it from an Electrical Engineer stand point.
 

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1985 500SEC; 1984 300TD; 1984 300CD; 1985 300CD; 1978 280CE
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You can have a complete circuit without charging the battery. If you replaced the ground cable with a 14 guage wire, you would have a circuit, but no charge. Same thing if the connections to the battery are corroded or loose.
 
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