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I was assuming that what our friend was really asking was what each of the terminations on a BMC engine were for rather than a wiring diagram for his boat's full installation. Of the latter there is little chance of there being any. The point I was making was that there are a number marinisations and many cases over the years a lot of those have been modified without any documentation so really it is a case of going back to the starting block and tracking things back to source. You really need to find a yard which is still servicing BMC engines for their own fleet or other customers to help.
Hi Guy As Bill said engines don't have wiring diagrams your bmc engine if it has lucas wiring colours the + pos on alternator is thick 50amp and is red or brown you could have two if high output alt, earth or - neg term is black the ign term is white and goes to ign warning lamp the W term is white/black and goes to rev counter you need to smear some vaseline on the terminals and wire ends before you crimp and push spade terminals back on alternator this will stop corrosion and high resistance. boat builders have their own colour codes as they buy wire on drums normally red is live and black is neg/earth plus all colours there after. John
Thanks everyone, I found a drawing under the aft cabin bed in a storage locker which I rarely use. We removed, cleaned and replaced all the connections and smeared with vaseline and now the refurbished alternator is working fine as are all the dials and warning lights.
The drawing is a generic drawing which I will bring home on my next visit and scan into my computer and if anyone wants a copy will email it to them.