Battery light glows brighter with higher RPM
 

I changed the belt (it was dry rotted and slipped when wet anyway), but the problem remains.....I think it is likely a bad voltage regulator, and I want to see if anyone on the forum can validate this guess...

It glows dimly at idle and gets brighter as I press the throttle.

odd. usually when the regulator fails, the light does not come on. it's the simple thing to try though, so it's always the first thing I try when the alt is not performing.

OK, ordered one from Phil....
The output is low - like 12.7-13.2V.

when I had the dreaded glowing idiot light problem it turned out to be the main wires from the alt to the battery that were bad. I put a wire from one of the big tabs on the alt direct to the battery & it fixed it. A bad connection on those wires can soon destroy a reg.

I made the below Alternator Test Cord.

If my Alternator works with this Test Cord Installed I know it is not a problem with anything on the Alternator.

I got the Alternator Connector at the Junk Yard but you can buy the parts at the Dealer and you need a 3 watt Light Bulb.

Im having the same problem. I also replaced my belt and the issue persisted.
You can read my post on it:
http://www.peachparts.com/shopforum/diesel-discussion/304541-voltage-regulator-again-1987-300td.html

I will have my resolution posted as soon as I have a resolution.

Vstech - my experience on my 81 300SD was different. The red light glowed faintly all the time and brighter with higher RPM. I replaced the voltage regulator(?), the easy removable thing that fits into the alternator. Did not help. Turned out that the alternator had gone.

So I am wondering if his problem is alternator.

PS - dear old Sears checked my system before I made the repair and said both my voltage regulator and alternator were fine. :eek:

When Sears Checked was the Alternator on or off of the Car?

This is from my notes and from one of our forum members:

ALTERNATOR DIODE check with volt meter
With your meter across the battery, on Volts DC, you should read 12.5 - 14VDC

If not, set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure. If VAC is OK but the VDC is not correct, then the problem is with the voltage regulator.

Not from my notes;
These Alternators seem to be sensative to grounding issues.
Where one if the Screws goes trough the Voltage Regulator there is a grounnd strip that presses against the Alternator Casing/Frame. If the Frame area is corroded it will not ground well.
Besides the Battery to Chassis and Chassis to Engine Ground Straps needing to have good contact I am beginning to wonder from what I have been reading if the Alternator Bracket to Engine areas are also getting so rusted that are providing the Alternator attached to them with a poor ground.
Layback40 suggested a separate Ground Wire going to the Alternator frame as well as replacing the Wiring to the Alternator if your problem does not go away.

I've had dim flickering charge light before. It ended up being the alternator. I changed the voltage regulator, no dice. Made sure the plug was clean and connected, no dice. New alternator fixed the issue.

I've also had it just be the voltage regulator.

It was the alternator itself when my SDL did that.

All three of my cars (190D, 240D, and 300D) did that more than once, and each time is was a dead, or dying alternator. Usually they are rebuilds from Delco, and there was a bad series of diodes, which Pierre replaced on the 240D, without removing the alternator (R & R is a real *itch!!!!). I would start it, drive to a shop, and have them test it while running. It should be between 13 and 14 volts. The lights wil l come on when it drops below 12 and a half . . . somewhere around that. General formula = 2.1V or greater per battery cell (6), for a mimimum of 12.6 Volts. Places that sell batts will usually do that test for free so they can see you a $600 alternator . . . .LOL, yeah, right!!!!

Good luck!

Torie

Diesel 911...can I check for continuity between the alt body and engine block or neg batt terminal to style in or out grounding issues?

When Sears gave me a clean bill of health, the alternator was tested on the SD. From everything I see in this post I think the alternator on the original poster's SD has gone bad.

Update: I changed the volt. regulator and it had no effect. I changed the alternator and it solved the problem.

Thanks everybody,