Hi

I've got a 17ACR alternator which I've had in my car for years.

The other night I noticed that the ignition warning light was slightly glowing. It cut in and out a couple of times but was generally glowing.

I checked the voltage from the terminals on the alternator and was getting 14.62 at the two bigger connectors and only about 10.8 volts from the little one (which I believe goes to the warning light).

Does anybody have any idea what this means?

I read on one website http://www.mgb-stuff.org.uk/electricstext1.htm#faults, specifically http://www.mgb-stuff.org.uk/electricstext1.htm#diodesthat this might indicate that some of the diodes in the alternator have packed it in.

Cheers,
Simon

If it's intermittent, I'd guess that it's the brushed getting short - they won't always get a good contact. Or do you mean they glow when the car is off? Then it's the diodes

14.6V is a bit high - I'd be worried about overcharging your battery at that voltage. It shouldn't do much more than shorten the life of your battery, but a modern alternator will sit at around 14V.

My old 18ACR? put out 14.5, and it was playing up a little, so I swapped it out for one of convertable mini's alternators (he's a member here) and it's been working fine since. If you're reading 14.6V, and your diodes need replacing, I'd just get a upgraded alternator with a good transistor regulator (read: any newer alternator).

If you do want to re-do yours, you can solder new diodes in yourself cheaply and easily, but the regulator is non-serviceable, and you may need to get a new one.

Hi Mr Yobbo,

Thanks very much for your reply.

I've PM'd Convertible Mini to check on costs etc. and have also been talking to John Smidt about whether it's worth a repair.

I might have to go the new path as I'm a crap soldlerer.

Thanks again,
Simon