1953 M21 electrical problem

[Jezyorkshire]

Got my 1953 M21 last Monday which is a complete runner and in good condition, have ridden about 40miles so far, last one I had was about 30 years ago.
The guy I bought it from was selling it on from the previous owner who said it had been used with no battery, before he delivered  it he had the engine oil changed and a new battery fitted.
All the lights work but the ammeter moves over to the positive when lights switched on, it also behaves exactly the same when the engine is running with lights on, could this be due to the battery being connected the wrong way?
Don't know if the Dynamo is charging as the ammeter doesn't move when engine running regardless of lights on or off, Jez

[idie]

Check the wiring to the ammeter.

[berniej]

The standard wiring could have been modified in several ways but if still original  i.e. 6V +ve earth then maybe:

The ammeter is connected the wrong way round
The dynamo needs re-flashing - here's a good article on how to fix it: https://www.matchlessclueless.com/electrical/lucas/repolarising-lucas-dynamo/

Checking which battery voltage and which terminal is connected to the bike frame would be a good first check before making any other changes.

Cheers,
Bernie

[Jezyorkshire]

Thanks for reply's, to be clear the previous owner rode the bike with the battery removed, I was sold it through a third party and he had a new battery fitted by a mechanic who didn't know the polarity so best bet is that the only thing that has been changed is that a battery has been fitted ant it's 50/50 wether the polarity is right?

[maddogmargetts@yahoo.co.u]

I took ownership of an M21 from 1958 and I found that it had a new solid state regulator replacing the old one but it had been wired wrongly with a negative earth so obviously the electrics did not work. The battery was a 4Ah which is also incorrect. So, the battery for our bike should be 12 to 14 Ah and is likely to be positive earth - the red cable from the battery connects to the frame. If you fit a modern regulator which is strongly recommended the best is DVR2 and costs around £40. Then wire it up according to the instructions written on the regulator itself, using one of two wires depending whether you have 6v or 12v. I suspect it will be 6v unless converted. If your dynamo and wiring are ok your electrics will then work. If not it will either be poor wiring/short circuit or more likely your dynamo. For £60 you could send this to Priory Dynamo's and get it checked out, along with minor repairs. I sent mine off and had new field coil fitted along with the armature reconditioned, new wiring, new brushes, etc. It works beautifully and the rebuild was £175. Well worth the investment. You can run the bike in daytime and not bother with electrics but you will not really be road legal having no horn or rear stop lamp, although I doubt the police would lose sleep over it. Personally I like things to work as they should. Hope that helps.

[Jezyorkshire]

Swapped battery ground over, it is now positive earth anf the ammeter swings the correct way, flashed the Dynamo and shows a very slight swing on the ammeter, will have a look at the Dynamo later, thanks everyone

[Jezyorkshire]

Done test for output/charge on Dynamo, not a sausage, will contact  Priory Magnetos

[Jezyorkshire]

 Decided to have a go myself after talking to a local guy who lent me some tools, stripped the dynamo and gave the commutator a good clean and replaced both bearings, spinning with a drill lit up a bulb so proceeded to refit but still no charge.
Ordered a new regulator from A.O.Services, the VReg 2b, £52 posted, wired it up and worked straight away showing a charge on the ammeter, might take to a classic bike night tomorrow after a test run if all ok