Many thanks for all your replies.
I am indeed a new boater with a bit of a nightmare from the previous owner who was a bodger.
Everything in the pictures is basically all of my electrics. I'm thinking about stripping all wiring out so an engineer can just come out and do a basic wiring job. All I've got in the is water pump, LED lights, two solar panels, electric water heater and an inverter/ charger as seen in the pictures.
Atm I have to drive the boat with the fuel cap on otherwise it won't start.