Yes indeedy ....
Thanks @Flip for explaining why it burnt out .... makes sense if it is only 6A
and many thanks to both of you for taking the time to help - glad to see the willingness to assist is still alive after all the years
I will order one of the diodes suggested at the correct rating and add it back into the circuit where the old one was and then I may even change the insurance to road use (rather than storage) and actually take her for a spin or two