420G red ignition lamp on when driving, but only very faintly

This seems to be an old topic, but nevertheless;The car has a modern Bosch generator with integrated voltage regulator, and a Volt meter on the dashboard, rather than the stock Amps meter.
The red light is strong with ignition on, but the engine off.
When I start, and then drive the car, the red lamp remains on but at a fraction of the power. Hardly visible on a sunny day, but definitely in a garage or at night.
Any thoughts?

In that case your generator is not loading anymore.
I would measure the voltage, it should be larger than 13,5V
What is your voltmeter level?

Peter Jan

I measured it with an instrument. 13,8
So the new geberator is fine.

Hi, i had an identical problem with my Daimler dd6. Charged alright (like yours) and a glimmering ignition light. It turned out to be one of the diodes in the alternator rectifier that had a bad contact due to oxide in the mounting plate.
Br svante

Interesting. Thank you.
How old was your alternator when tgat happened? Mine is 2 yrs old

Probably it was the original alternator with 80000km as i bought the car 30 years ago. After a few years running with the glowing Warning light I removed the diode, cleaned it and pressed it back again. I think there were 9 diodes and if one
is not doing its job you get a glimmering light. It was pretty well described in the workshop manual as I remember.


Hi Peder did you solve your issue with the light?

Not yet. The new Bosch alternator needs to come out and be opened on a work bench, to clean the diodes.

If its the red ignition light on the dash it has nothing to do with the generator, the light is activated by an oil pressure switch so when the engine starts and has oil pressure the switch cuts the light. Mine was playing up and I changed the sensor unit and problem solved.

Update: as of a month/4-5 drives ago, the faint red light has disappeared when driving. (It is fully on when I turn on the ignition, and shuts off when oil pressure is normal after starting).
Have the oxidised diodes in the modern Bosch alernator cured themselves…?:joy:

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This is the car. Found it for sale on thr JCNA site a few years ago with just 2 owners. Original paint which is rare, and proves how the Germans got it wrong on a 420G and S1 E-type which I also own. Both were restored in Germany and the opalescent dark green lacks sufficient green. Too grey.

Hi Peder,

Yes, and original paint may (and pretty much must) be a bit faded.

What I have been saying for 25 years: the modern matches for ODG are not dark enough and not green enough, too much silver snd grey

Nice car. 8)