Engine 1500 sp running sweet.

Idles 850~950rpm

Rebuilt non Bosch dynamo... German rebuild though

Once engine has warmed up and settled down red light comes on. Once I tickle the throttle it goes and same when driving but once revs are down on again.

Only other thing is during my mot the tester made me rev the engine to get the headlights through the brightness test..

My question is is it the battery regulator or the tesco value dynamo that's at fault?

Thanks Philip

I would put a tester across the battery and see what is going in at idle and when reved, 12.7 and up to maybe 14v . if that's ok maybe suspect faulty battery. my red light will come on sometimes when at idle. very slow tickover which I like.

First off, double check its not the oil pressure light incorrectly wired up.

I had exactly the same problem several years ago when I replaced a Bosch dynamo with one of the cheaper repro ones. It was basically OK but from the very start, at idle the red light came on. Like yours, once the throttle was on a little bit it went out. Also tried a different regulator – no difference. The replacement dynamo only lasted a couple of years but I replaced it with a (more expensive) recon Bosch unit. This not only looked better quality (subjective, I know) but as for the original unit, the red light at idle was banished. No problems at all since then.

It is normal for the red light to come on at idle revs that is why alternators were invented!!


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Stevep wrote: ↑

Mon Nov 12, 2018 12:42 pm

It is normal for the red light to come on at idle revs that is why alternators were invented!!


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Only when there's something wrong.

When I say the light comes on a flicker is more accurate.


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Thank you for all the advice.

I have just bought a new battery as it appears the old one is in bad shape...I should have checked it straight off but it was relatively new. I guess months standing idle plus all my other adventures ( burning out my last dynamo ) have taken thier toll.

As for the wiring everything is in order there as i have been going through it sorting problems with starter motor, oil pressure sensor, temp gauge etc

Thank for the help, again!
Philip