Battery Light

[ludwig]

The battery light on a 1982 300D is acting funny. I noticed it at first last night when I shut down the car and with no key in the ignition, the battery light was on. I then started the car and I smelled some thing burning, couldn't pinpoint where it was coming from and eventually the smell went away. Now the battery light does not come on when the engine is shut down. When the car is idling, the battery light is not on. But when driving and the rpm goes up, the light comes on.

Alternator is a fairly new rebuilt with 30,000 miles. I swapped out the voltage regulator with a known good unit and still the same light activity. I even disconnected the negative battery cable while the engine is running to see if the head lights would be still on, and they are. It appears the alternator is charging. Any thoughts?



.

[Diesel911]

Disconnecting any of the Battery Cables while the Engine is going can harm the Alternator.

Since when it works normal the Battery Charging light is connected to the Alternator through the Ignition Switch it could be an indication that the Ignition Switch is on the way out.
Or, the Lock Tumbler and the Mecanism in between that turn the Ignition Switch are some how fouled/worn up and not allowing the Ignition Switch to return to the proper positions.

I suppose it is possible for there to be cracks in the wire insulation in the under the Dash Wiring that could ground the circuit.

If you remove the Alternator Connector there is 3 slots. The Single Small Slot (Blue Wire) goes to the Battery Charging Lignt and when it works normal there is no Voltage there until you turn the Key on.
The other 2 larger Slots (2 Red Wires) always have Battery Voltage.

It might be handy to know what sort of voltage you are getting when it is charging.

The Voltage Rebulator controls the Field Circuit by grounding. If your where your Battery Cable bolts to the Chassis Chassis Ground or Engine to Chassis Ground is not connected well or the Alternator Connector is corroded I would expect the Alternator all sorts of abnormal stuff.

[ludwig]

Thank you for the response.

How do you test the ignition lock?

I'll check the ground and power connections for corrosion, and I'll have to see how much voltage is coming out of the alternator.

Thank you again.

[TX76513]

The resistor pack in the alternator is bad (one diode anyways). Its allowing current to flow backwards from the battery. Cheapest route to repair is an alternator shop or DIY if you have cracked one open before.

[Diesel911]

If you remove the Alternator and take the Alternator for a free test and it test OK it would have to be an issue with something in the Circuit.
I know that the type of test done at AutoZone would tell you if it was Charging OK but I do not know if a Bad Diode would show up.

Places that have an Alternator Tester that has a screen that shows the Wave Form of charging Voltage/Current would give more information.

Changingl the Ignition Switch is a lot of work and at least one person has found that after changing the Ignition Switch that it was actually something in the Steering Wheel Lock that turns the Ignition Switch causing the problem; not the Ignition Switch itself.

DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

[lutzTD]

Originally Posted by Diesel911

If you remove the Alternator and take the Alternator for a free test and it test OK it would have to be an issue with something in the Circuit.
I know that the type of test done at AutoZone would tell you if it was Charging OK but I do not know if a Bad Diode would show up.

Places that have an Alternator Tester that has a screen that shows the Wave Form of charging Voltage/Current would give more information.

Changingl the Ignition Switch is a lot of work and at least one person has found that after changing the Ignition Switch that it was actually something in the Steering Wheel Lock that turns the Ignition Switch causing the problem; not the Ignition Switch itself.

DIY Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/Wikka/DoItYourSelf

they can test the alternator without removing it if you can get the car there, saves a lot of cursing getting that darn bracket loose if you dont have to

[ludwig]

I'll go to my local parts place to see if they can do an alternator test in the car. It's a shame because the rebuilt alternator is only a few years old.

Thanks for the input.


.

[sjh]

Those are classic signs that your alternator needs help.

I'm surprised to hear (but I have no reason to disagree) that running the car without a battery connection is damaging to the alternator.

PS - When this same problem happened with me the smell you describe was the electrical components burning up in the alternator.

[smiffy6four]

As far as I know the only way to check the diodes with the car running is with an oscilloscope. Or an mutlimeter on each diode(with the alternator dismantled)