No output from alternator

[boiler]

Hi all. This is just something to consider when changing the bulbs in the warning light cluster or more specifically the ignition warning light. I changed the bulbs recently but discovered a little later that the battery wasn't charging and the ignition light was staying on. The wire from the alternator to the ignition warning light requires enough current to start the alternator working as it is connected to the field coils. Once the alternator is working it generates its own power to operate and regulate the field coils. My problem was that the bulb I fitted was of a higher resistance than the old bulb which would restrict the current and produce a voltage drop of sorts. It measured about 30 ohms whilst the original is about 10. Anyway refitting an old bulb restored operation. I didn't suss this straightaway I had to research a few circuit diagrams and read about alternator theory! This may be obvious to some of you so this post is for those like me who usually create another problem when dealing with the first!

[Guppy916]

I learnt that way Duncan at Classic Car LED's put me right, the alternator red bulb is the only non led on my GT6

[RobPearce]

It used to be a common bodge, if your alternator was a bit weak, to fit a brighter bulb. Draws more current when lit, meaning the alternator starts up a bit quicker.

[iggy]

Good bit of info though i will  probably forget by the time i ive got to change that bulb😳

[Guppy916]

don't worry Gav we are all here to remind you 

[Gt6s]

Correction. Power runs to the bulb. Then to the alternator. Not from the alternator.

Laurence

[DJT]

Modern 'non-exciter' alternators don't need the ignition light to function. Just tape the small brown/yellow wire out of the way. The ignition light still works as it should.