As Don-Spada said, is the charging light on? This bulb needs to be working.
Thanks Don, reply sent…
OK lads, settle down, after very careful consideration. I’ve decided to get me matches out, and fire up the BBQ, get a pile of burgers on the go, and get Keith and his Brother to sort it. Bloody thing’s doing me sodding Ed in… 
The light comes ON when I throw the switch, then shines dim when the engine’s running, goes a bit dimmer when it’s revved…
I’m giving up now, it’s beat me, I can only take so much, ya know… 
I’ll be back with whatever the lads find, OR I’ll tell you how long it lasted with a Swan Vesta in the tank, either way, I’ll be back…
If the light is coming on then glowing with the engine running it sounds like it is producing something but not enough.
The earth lead connection on the gearbox mentioned earlier is the other end of the big thick -ve wire from the battery. It bolts onto the gearbox under the battery tray. That connection can go fuzzy some times and need a good clean.
Good luck. Hope Keith can save it from a fiery death adrift in the Medway.
i fitted one of these - as i am a plodder i found that within 3 weeks the battery was loosing its edge - and needed charging – https://www.euromotoelectrics.com/Articles.asp?ID=135 or there is this one as well Stator Kit for Moto Guzzi 1975 - 1992 - Bosch alternator replacement kit
where the standard is max 20 amp at full revs these 2 replacement both are capable of 20 amps at as low as 2000 revs and up to 29 amp at 5000 revs
once fitted i never had a flat battery again
Could also be that the alternator commutator needs cleaning or the brushes need replacing?
will be checking everything later this morning,i do know it,s only putting twelve and a half volts out and back
As has been posted, the light coming on and then dimming means it is working but not adequately.
Check your 3 phase connections both on the alternator and into the diode pack.
It is worth making sure the diode pack is properly earthed.
If there is no multi earth connection under the battery tray find out where it is and clean it.
Hope that helps.
Ok lads, now for the update…
Investigations have found that the alternator brush holder has a small hair line crack in it, therefore, the brushes are Bouncing and not making a proper contact… 
A new holder and brushes have been ordered, and around the corner is a company that sorts these sort of things out, so I’ve given the lad the ‘Heads Up’ cos I’ve not got a soldering iron man enough for the job, he has. So HOPEFULLY very soon, all will be well, but BOY… What a bloody wind up…
Perhaps I shouldn’t use the bike as an every day commuter, if it was a play thing, I’d not get so stressed when it plays up. Don’t think people use bikes like they used too, when I were but a lad…
As I have 2 Guzzi’s and no car they are also my everyday transport, shopping trolley and and weekend fun.
It is a bad day I don’t ride one of them.
Well done, I thought of brushes as that was the cause for me when the charging light went dull but not out when revved
Well done n finding it. I thought you changed the brushes and stuff when you first dug it out of the old barn.
And now for the continuing saga… 
All Earth wires have been cleaned and bolted in place, battery/diode board/regulator and the brush holder along with brushes have either been replaced, or swapped and checked…
And…
It’s STILL not charging…
Oh how happy I am, floating around like a butterfly… Look it’s driving me mad, MAD I tells ya, mad… 
Have you tried putting a different battery in it?
Just a thought.
yes we did,other day in the garage we did get 13.5 volts by holding the brushes against the rotor,thats why the new brush holder
only thing left to change is the stator
This one is being a nightmare to track down. Did Shaun give you the test thingy I sent him to try. It gives a few checks to carry out.
Weak brush springs??
did all the test plus a new brush holder and brushes
What the HELL is wrong with this bloody bike… 
Swapped out everything that can make or retain sparks, and just now, swapped out the last thing, the Stator with a known working one. And STILL the Bar Steward won’t charge…
So apart from all the Earth’s being done, and the diode board, regulator, rotor, Stator AND Battery, being swapped. Is there something ELSE that I can attempt…
HELP, it’s getting REAL close to Bonfire Night, and I’ve got a box of Swan Vesta waiting…
Very strange as to what’s causing this.
What is making you think it isn’t charging? Are you checking with a voltmeter across the battery?
Faulty battery? Although Keith said he tried another.
He did manage to get it up to 13 V by pressing down on the brushes so that does make me wonder about them.
Have you tried cleaning up the slip rings with some spirit, including cleaning between the rings.
Check the resistance of the rotor.
Clean the battery connections, particularly the biggish red wire from the diode board rectifier to the battery.
Check the really big -ve lead where it connects onto the frame, somewhere down below the battery box.
Have you checked the regulator on the other side? The tin box with the tape around the bottom. They are usually pretty reliable, but may fail occasionally.
Check the continuity of the three yellow wires from the stator up to the diode board, incase there is a dodgy connection somewhere in the loom.
Check the charge light is getting a good supply voltage and then onto the alternator unit.
Have you got the blue wire connected onto the spade connector that disappears into the stator?
Purple wire connects to one of the brushes, the other goes to earth.
Flash the rotor. I put +ve to one ring and -ve to the other.
Thanks Don, I’ll give it all a go, by the way its a volt meter at the battery, 12.5v no engine running, 12.5v revving it’s guts out…
A Rally in Belgium on me War BSA, this Friday, so this thing will have to wait… 