In my experience if the brushes no longer contact , then the red ignition light will illuminate.Quote:
I have the exact same problem with my D2a V8 and I am putting it down to the brushes in the alternator being worn out
When the alternator died soon after I bought my car (probably partly caused by the battery terminals) the light would come on at low speed then go out when revved.
I opened it up and found the brushes gummed up by oil from the camshaft plug and worn out.
Regards Philip A

