9 replies to this topic

[AlasdairM]

Hi folks

1990, 1275 cooper. 100000 miles.

I’ve had my cooper running on the road all summer, after it sitting for 13 years.

Just the other day, the ignition light stayed on faintly after I started the engine. It didn’t change brightness with revs, and it gets brighter when I turn on electrical components. So I checked the condition of the fan belt, and it was a bit worn. So I replaced the belt, and the light still stays on. The belt is the correct tension etc.

I checked the voltage over the battery, and it’s 12v exactly. The voltage doesn’t go up when I start the car. I checked the voltage coming out of the alternator, and it’s also 12v.

So it seems like the alternator isn’t doing it’s job properly, and my oversized battery was just taking up the slack.

Is it most likely a worn alternator? Will I just buy a new one (£60 from minispares)? I’m not sure what else to check- I’ve read the other similar forum posts on this issue...

Thanks

[KTS]

worth checking the plug/terminal connections on the cables between the alternator and starter motor/solenoid to make sure they're in good order

[71Green-Clubby]

hey, yes it sounds like the  alternator is shot if there is good connections, you should have  over 12v after start up 13.8-14.3 is a good value to have coming out of the alternator

[AlasdairM]

thanks both. Connections are all good. 

 

I think Eurocarparts is actually cheaper than minispares, since they give you money for your old alternator. 

[croc7]

Sounds like the alternator needs to be replaced, a good battery should have about 12.5V at rest, 14.4V when charging from the alternator.  You might want to check the engine to body ground as well.  I had a faint glow from the ignition light and the solution was to clean both ends of the grounding cable.

[Spider]

Sounds like the brushes are worn in the Alternator.

 

Depending on the model of it and the condition of the rest of it, Brushes are quite cheap and easy to replace.

[bluedragon]

Unless you live in a remote, isolated area with no car parts vendors nearby, just remove the alternator and take it to a shop to have it tested. Every shop I've ever seen tests them for free. I believe this is a Lucas A127 internally regulated alternator?

 

If you want to test it yourself there are steps you can follow if you've got a good multimeter, and ideally an ammeter that can handle a 40-70 amp load, but a shop with a test rig is the easiest way to go.

 

 

Dave

[AlasdairM]

Unless you live in a remote, isolated area with no car parts vendors nearby, just remove the alternator and take it to a shop to have it tested. Every shop I've ever seen tests them for free. I believe this is a Lucas A127 internally regulated alternator?

 

If you want to test it yourself there are steps you can follow if you've got a good multimeter, and ideally an ammeter that can handle a 40-70 amp load, but a shop with a test rig is the easiest way to go.

 

 

Dave

 

 

Ok thanks Dave. I'll take the alternator off on Monday and see if a garage will test it for me. I'm in Glasgow, so should be able to find one somewhere! £50 for a new alternator doesn't seem too bad though. 

[slidehammer]

If it worked ok prior to lay up I would suspect the brushes aren't making good contact on the commutator, might be worth taking it off and cleaning the copper commutator with a contact cleaner and checking the bushes are making good contact. They might have got gummed up and not sliding forward properly under sprint tension. 

[AlasdairM]

for completeness, I ended up charging the battery back to 13.1V. 

 

I then took the alternator off, and cleaned the contact points, and where the brushes contact inside. I reassembled, and everything appears to be working fine now. The alternator and battery now read 13.8V/14V when the engine is running. 

 

I should probably try and fit the plastic water guard over the alternator, as I'm sure this will slow down the corrosion inside the alternator and connections. 

 

thanks for the help. 

Edited by AlasdairM, 13 October 2020 - 01:17 PM.