Well said Jake,I know that any information is good but sometimes it gives you a bigger problem.If a person that puts up advice and explains why they came to a answer to the problem then it’s a lot better.I myself have been desperate and would try anything and ended up with more problems,Keep up the good work lads it’s always good for the group.As you have said, looks like the wiring colours changed for the American market as there is no "white cable" anywhere near the speedometer on my British market cars.
The wiring diagrams show that the "white cable" replaces the green wire not the red/green wire. The red/green goes to the speed generator and speed control.
The white wire comes from the petrol pump relay on American market cars, which in turn is fed by fuse 2 on the fuse board.
The wiring diagrams I am looking at were printed in May 1980.
If that is no help, look at early SZ model cars as the Spirits were a continuation of the Shadow 11.