Morris Minor Owners Club

Dynamo tested and charging,spade connections seem good, light slightly dims on reving BUT stays on?

have you got the connections to the coil the right way round

Swapped coil connections over, light still on

I would suggest that the dynamo brushes are on the way out or that you have a faulty control box

Is the dynamo polarised correctly?

Check the battery voltage first when revving the engine - What is the reading? It should be around 14.0 volts to charge the battery. If you are getting less than this check the output directly from the dynamo. If the dynamo is putting out a significant charge (but it's not reaching the battery) then the problem will probably be with the regulator box. They can be adjusted but it is fiddly to do and might be quicker and easier to change it for a new one or known good secondhand one.

I second the vote for brushes - give it a thump with a hammer - sometimes jolts the brushes into contact and may keep you going until you get the new brushes.
Alternatively - I do have a spare dynamo - PM me if interested!