Alternator warning light staying on

[itm]

The red alternator light regularly stays illuminated in my 94 Griff 500. I remember being told a long time ago by Redhill TVR that this wasn't unusual, and was caused by feedback current from the alternator. Has anyone else had any experience of this?

[old64er]

is it still charging?

[SteveGRF]

This may be stating the obvious, but have you checked the 100 AMP fuse & connnections under the car? this could be the cause, warning light on = flat battery. Bloody obvious I hear

[dickymint]

Do you mean it stays on with the ignition off?
If so the diode pack has failed in the alternator....eventually the battery will drain.

[thatch]

My Red Warning light stays on constantly (when ignition on) when driving. (Griff 4.3 BV 1991) Mentioned it to my garage ages ago, who told me to ignore as everything was working fine!

I, perhaps naively, was reassured!

[itm]

Yep it's still charging (I had a new alternator fitted a few years back, and this symptom existed with both old and new alternators).
The red light only stays on when the car is started.
Interesting to hear of at least one other Griff owner who was told "not to worry about it"!

[GreenV8S]

It is most definitely not normal, and it is something that I would be worried about. The bulb is connected between the switched ignition feed and the alternator coil. It will come on when there is any voltage difference between these two. If the ignition is off engine stopped, both are at 0V so the light stays off. Switch the ignition on engine stopped and current will flow from the ignition to the alternator, lighting the bulb. This current also helps jump-start the alternator. Ignition on engine running both should be at full voltage (13.8V) so the bulb should stay off. Ignition off engine turning (for instance as the engine spins down when you switch off) current will flow from the alternator to the ignition, lighting the bulb.

There are three common failures: if the alternator stops charging, the light will stay on while the engine is running; if the rectifier pack fails, the light will stay on after you switch off and the engine stops; if there is a significant voltage drop on the switched ignition feed the light will glow dimly while the engine is running (this will normally get brighter if you increase the load on the switched ignition feed by turning on more electrical accessories).