Broom Ocean 30 wiring diagram ?

Why not write to the Brooms boat building company who are Based in Brundall in the fine county of Norfolk.

If you go to their web site I am sure they give the postal address or Email them!

Good luck with that.

All of those vessels were hand-built, often by different boatyards, and the construction plans and wiring diagrams were also hand-draughted before the days of modern CAD. After production ceased the plans were variously thrown away or manually filed away to be eventually lost when the manufacturers ceased trading and disposed of everything.

So you're highly unlikely to find them online.

The other major problem is that the construction plans and wiring/plumbing diagrams were seen more as being a general guide than as something to be followed exactly. Just like kit-cars it's very rare to find any two which follow the plans exactly as during construction builders tended to take short cuts, make non-standard modifications and even improvements where it's sometimes clear that what the diagram calls for is plain wrong or unwise. With regard to wiring, each boat sparky has their own way of doing things and if materials are short during a job it's not unknown to find that even the wiring colours are totally wrong, with just coloured sleeves at the wire ends if you're lucky to indicate what they should be.

You also have to contend with the fact that after 30-odd years, the original wiring may be significantly different to what went in to begin with, and could have various additions and usually plenty of bodges.

All that is reliably true is that just as with GRP-bodied cars, the wiring is twice as complex and far more prone to faults as there's no earth return channel through a steel body and all earths therefore need wiring as well.

I therefore suggest that you swallow your pride and enlist the help of an automotive electrician who has experience of GRP bodies, and make sure that they are familiar with the current contraction and use regulations for British watercraft (similar idea to your IET Regs, but entirely watercraft-specific). Better if you can find a sparky specialising entirely in watercraft but most are just automotive sparkies with additional qualifications. What you pay will save a fortune in lost time and headaches, may prevent a fire, and will help when you need to get the boat certified for use on UK waterways again. You may even be able to trade professional favours as most automotive/boat electricians are poor at working on mains AC installations (you'll never find one who admits that though...).