Morris Minor Owners Club

Hi All,

I have a faint glow on the ignition light on the dash.

The readings under the bonnet are as follows:-

(All at fast idle)

Battery 12.4v
Dynamo output (D and F terminals bridged, Multimeter -ve lead connect between them and +ve to good earth) 12.2v

According to the haynes manual these should both be about 14.5/15v.

The dynamo is less than a year old do it seems strange to have such a low output already.

Does anyone have any ideas/tips on this? I don't have another to test it against. Could it be wiring in the car?

is the fan belt tight enough,but looks like dynamo is done for,if its under a year old it should be under guarantee,take it back and get it replaced. and nothing to do with wiring,except connections to the dynamo,battery,control box should be checked.

Yes the fan belt is tight, I can turn the engine over from the fan!

Unfortunately the previous owner fitted the dynamo and didn't pass on the receipt!

Alternator conversion looks likely then!

To check the dynamo remove the two conecting wires(Yellow & Yellow/Green) and short the two dynamo terminals together. Measure the voltage to earth, should be about 20 volts. No need to race the engine fast tickover is good enough.
If its gone fitting an alternator is easy and you can then forget about the control box, but you can leave it in to look original if you wish.

Probably just stuck brush...worth checking before laying out cash on a replacement.

Removed the dynamo, inspected the brushes etc. Nothing seems out of place. Refitted and same issue.

Worth a try though.

Time to get the wallet out!

Did you test the dynamo by running a wire from the battery to the two joined terminals? If it runs as a motor - it's fine. The problem then will be with the regulator box - or even just a bad connection!

I have tried a proven dynamo and it is still returning the same issue.

Where next? I have played around with the adjustments in the regulator but it seems to make no difference, could it be a replacement there then? Or is it something like a bad earth?

Thanks

It's always possible - but at least it does look like Reg problem.... Maybe someone has a good/secondhand one you can try - if it works - then buy!

You say it's a proven dynamo, did you test for 20 volts out with the terminals connected to satisfy yourself that it is. If all seems ok then it does point to the regulator, if the wiring is correct.

I'm not convinced about that '20 volt' test - the SURE test is to run it as a motor - if it runs = it's fine !

I dont want to get into motor theory here but if there was a short circuit winding on either the field or the rotor windings then it could still run as a motor, not for very long though, but you would definitely not get the required volage output of 20 volts.

I think I would be looking at an alternator conversion.

I don't see what would limit the volts to 20 ?? Surely they would just climb without limit until something breaks down! I've always found the motor test a good indicator - if it doesn't run as a moor it certainly won't work as a dynamo. The other test is to join both terminals and connect to the battery with engine running - this puts it on full load and should pump the battery up to 14 volts quite quickly. My guess is it is a Reg problem.