Rory -

Here's a photo of a clean board which can guide you....

TIPS

• The final wiring is so jumbled that a photograph of the wired board will not help you. Everyone's finished wiring looks like a "rat's nest". 

• The trick is to go slow and illuminate the inside of the HL shell with a bright light, otherwise Brown/Yellow can look an awfully lot like Brown/White. I highly prefer the "whiter" light output of a 4000K LED bulb when working with wire colors. This is highly preferable to the dull yellow of the typical incandescent bulb.

• I highly recommend that you lubricate the male prongs of the circuit board with electrician's anti-oxidation compound before plugging the female wire ends onto the board. Remember that you're re-making electrical connections using 41 year-old connectors. Connectors that have been exposed to and degraded by rain and wash water for decades. Such a compound is No-Ox-Id, but I'm sure others can be found on your side of the pond.

• The standard wire end connector is nothing more than a standard insulated 1/4" spade connector. These are commonly available at automotive and electronics supply houses, and also off the internet. The wire's insulation is stripped back ~3.5mm, and the terminal is crimped onto the exposed copper leads with a crimp tool. Each installed terminal should be tugged on to make sure the crimp is not loose and that the connection is tight enough to conduct electrical power. (Remember: You're trying to solve electrical issues, not create more.)

• Clearance space between terminals is at a premium. Work space can be tight. To hold these terminals during the plugging operation you may wish to buy a common hand tool called "duck bill pliers". These are like regular hinged pliers, but the tips are wider and flat.

• Generally, here's how the circuit board works... Connection is made between like-colored wires by plugging all wires of the same color to the male contacts within that same color zone. For some colors there are only 2, others 4 and 6. Not all areas end up completely filled.
- Power from the Green lead comes from the Ignition switch to Green and is passed through the 7A fuse to Green/Black. Same for Gray to Gray/Black. It is important to remember that anything plugged to Green or Gray is NOT protected by fuse. If you add lights or other accessories, then I highly suggest you add your own in-line fuse and provide separate protection for said accessory. 
- Green and Gray are turned OFF by the ignition switch. Red is a direct connection to the positive side of the battery, with NO fuse protection or ON/OFF control. Brown is the DC Return to the negative side of the battery (what you might call 'Earth' or 'Ground').

Hope this helps.

Thank you Richard, really useful info which I will take time to read in front of the bike. Thank you for the tip on the duck bill pliers ( never seen one of these)  and the anti oxidisation compound. 

Regards,

Rory