Morris Minor Owners Club

Hi Everyone, I came to take my '65 2 door out for a drive today and noticed that the ignition light started to come on when the revving the engine.
The ignition light comes on when ignition is turned on.
It goes out when the engine starts.
As the revs rise the ignition light comes on and then gets brighter as the revs rise.
I suspect it could be the control box but I am not sure how it should be correctly set up.
Could anyone offer any advice?

Fan belt loose ? Dynamo or alternator?

Fan belt is fine
I am running a dynamo
I have the old type control box with the screw connectors.
I have just had a look inside and noticed the contacts on the RHS coil were shut with the ignition off. With my limited understanding I thought these contacts should be open when the ignition was off so the battery didn't try to turn the dynamo (like a motor)
Any ideas?