Thread: Alternator light dull glow 110 TDI300

That means the alternator has a short across the diodes,mine did it a while back. Pat

Worn brushes perhaps?

The glow is caused by the difference in voltage between the ignition system and battery. My ignition light glows faintly at idle when I first start also but it generally goes out once the battery has been replenished after a little while driving.
The battery voltage of 12.5v at rest (let it settle for a few hours after fully charging) is in my opinion, low or the battery on its way out. A rough guide is 12.65v - fully charge, 12.45v - 75% charge, 12.24v - 50% charge, 12.06v - 25% charge, 11.89v or less - dead.
If the light glows dimly at idle after a bit of driving, I would suggest the battery is finding it difficult to attain 100% charge and may be on its way out. How long it will last, I couldn't say but I generally get three to six years out of a battery. The most used one's (daily driver long km's) generally last the longest.

Hope this is helpful

regards
Mick

At 14v, the alternator appears healthy. You don't want to charge the battery at more than 14v, you'll just cook it (boil it dry).

Thanks Fellas

Originally Posted by PAT303

That means the alternator has a short across the diodes,mine did it a while back. Pat

I had a similar dull light on my D1 200TDi - it was there at all RPM - turned out to be a failed diode in the regulator pack. The auto electrician couldn't get a replacement part to fix the original marelli - ended up with a new alternator.

My battery dropped a cell and the alternator was on its way out a while back all in one week.
Dull ALT light showing on both occasions plus the starter sounded a bit slow.
Might have been mind game though.
Now with twin batteries, I can could or drain 2 and pay twice the price.
Yeah, can't wait.

First check battery is holding charge and than charge voltage, should be around 14V I believe.
I replaced my alternator with a standard size for less heat output from them as I was told a few times that the bigger u go in charge rate the more heat and that shortens their life span too.

Hope u get it sorted.