I printed the wiring diagram for Europa Specials after 73083924R and it seems to exactly fit the car I am working on, 3755R. This I printed on an A3 sheet of paper in glorious colour, and all is now clear to me.
The white with red trace wire from the ignition key goes straight to the 12 pin open white plastic connector called the logic box. This is located by your left knee.
Then there is a yellow and pink wire which goes to a connector which was broken, by the back of the fuse box where the heater radiator is located.
Then this yellow and pink wire then goes back through the central tunnel, along with 14 other wires, and appears to the rear of the starter wires, with a white/red wire which goes to the starter, and two other wires, which must be earths for a start relay, which is missing.
So I need to short the white and red to the yellow and pink at the logic box, and fit a start relay to the rear right hand chassis rear of the starter motor.
Meanwhile the thick purple wire with the ring on it turns out to be an earth for the metal rail where the steering column attaches to the bottom of the wooden dash. This wire gets bolted to an angle bracket, along with other black wires, at the back of the fuse box, where the centre of the dash bolts to the tunnel.
I have traced every wire now, and the diagram called Europa Special Wiring Diagram (Federal) (Chassis No. 73083924R and above) is just about exactly what I have got for 3755R and presumably also 4129R which I am driving regularly. When I change 4129R to RHD, I will have to do all this again.
It is still a mystery what the grey/green and grey/blue wires do, but as I can see both ends of both wires, and they are only about 18" long, it doesn't really matter, but grey does not even appear on the wiring colour codes.