Just using my new Durite Terminal Extration Tool Set to dismount the speedo wires from the Corrado engine loom, as they're not in the Golf3 engine loom. Grrrrrrrrrrrrrr.
There are three wires:
A black wire, which goes into a common earth, which is black and white and goes back to a white plug, which has a central locating lug on the opposite end to the clip. Looking from the side the wires go into, working from the clip-end being the top it terminates second down on the right.
A white wire with a blue trace, which terminates in a second white plug, which has a locating lug on the right hand side. This wire terminates bottom left in this plug.
Then there's a brown wire, which terminates in a third, slightly wider plug. The brown wire terminates second down on the right.
Photos of the new tool and wires shortly (calm down everyone).