Amp light coming on when it shouldn't...
 

'67 Amazon running a later B20 with factory alternator.

The amp light has started staying on once the car has started, and often takes quite a while to go out (sometimes over 10 minutes......), and it's not just a glitch with the light as the battery is being run down. Just to make it even more fun to diagnose, this is intermittent but seems to be becoming more frequent.

Any ideas what could be causing this? The battery (Bosch unit as specified for a 240) is fine according to the built-in check light & the fusebox was recently replaced with a brand new one. All other electrics seem to be working as they should. Is this an alternator fault (e.g. worn brushes), or could there be a dodgy connection somewhere that might cause this?

I've had a look at Ron's excellent write-up but that appears to be only for the earlier dynamo & separate voltage regulator cars; or does some of it still apply to those equipped with an alternator?

Thanks!

Right im not 100% sure on these things but it does sound like it maybe an alternator problem. They have an inbuilt regulator that keeps the voltage at the right level depending on revs and current drawn.

Do you have a volt meter which you can check the voltage at the battery with when running?

Or a slipping fan belt?

Amazonista;

That's right...my article is directed at the early, more common system with an oe dynamo so troubleshooting info does not apply to an alt equipped system.

Your symptoms do sound like worn brushes...because of the decrease in brush height, springs cant give them adequate pressure onto the sliprings, and loss of charging results sometimes it seems to fix itself...but not for long...I would check brushes first...

Good Hunting!

Thanks! I've looked at the relevant documentation on www.volvoamazonpictures.se, however that only shows a Motorola unit with a separate regulator. Mine is another make (think it's a Bosch - will check later on) & has a built-in regulator. However is there much difference between the two in terms of the info in the factory workshop manual?

Also, does anyone know if the brushes are still available, and what are the best sources on this side of the pond?

If you have problems sourcing them; take yours out, measure them and then buy some of a similar size for another make and cut them down to fit yours.

If you get the details on yours ill check the one on my engine, if they match your more than welcome to it. (Will have to check the condition before mind you as i dont want to send a broken one to you.)

Scandcar list these Bosch brushes on their website.

222s...i had exactly the same problem with mine last year,after days of messing about checking things it turned out it was the alternator that was the problem,i also have a amp guage in the car and could see the amps dropping,especially when i put lights etc on.
i struggled to get new brushes and so did a couple of local places the recon alternators.
in the end id had enough!..rang rob at amazon cars and bought a new alternator,that sorted it!

i have a 1970 amazon B20 with Bosch alternator. Mine has a seperate regulator.Square unit next to relays on near side front inner wing.I fitted new brushes to overcome same fault.Brushes were £6.58 a set.Let me know tomorrow if you require them and i will look for receipt for details.I also have a new regulator.