Alternator Battery Light ?

[Steve300D]

Hey folks, (1984 300D)

My alternator isn't charging the battery, and I'm confused between what I've read on this forum and the symptoms I'm having.

When I turn on the key, the warning lights on the dash come on--except the battery light. My understanding is that this 3W bulb is necessary for alternator function. So I pulled the bulb, supplied 12V to it, and it lit. Why it doesn't light when I turn on the key is a mystery.

With car running, battery reads 12.36V. At the alternator, I got roughly 12V on the two big wires, and very little voltage on the little wire. I already tightened the belts.

Any help is appreciated.

[Jeremy5848]

There are a number of potential causes. Having eliminated the bulb, you should next pull the regulator and see if the brushes (which are part of the regulator) are worn down to nothing. If the brushes don't make contact with the slip rings you will generate no charging voltage and additionally the alternator light won't.

Less likely problems are diode failures in the alternator, broken wires in the alternator, or wiring problems elsewhere in the charging circuitry.

You can remove the regulator with the alternator on the car. You'll need ramps or jack stands, the work is done from underneath.

Jeremy

[sixto]

Shiny brush tips make good contact, sooty brush tips make not so good contact.

Sixto
87 300D

[Steve300D]

Thanks, guys. I'll report back.