Thanks Tony.
First off, I was instructed to turn the ignition key off when engine starts from gentleman i bought boat off. I was warned never to have red light on.
Oh dear!
I will try what you suggested in morning.
And no, I don't have a clue about a multi Meter but I'm moored in a club so I will ask someone to try for me when I see them.
In terms of banks I only have the one starter battery and nothing else. All my lights , pumps ect work off the starter.
Again, I will try it with ignition key on in the morning , give it some revs and perhaps turning key off was the issue.
Fingers crossed