As my speed sensor got snapped when I went over a mega bump I've bought an RS reed switch as noted in an earlier post.

Nice saving of £15 over the Robin Bar Steward CA version but it has three wires not two like the original.

They are Tan, Green and White.

The original has a switched live from the ignition and a return to the speedo.

Which is which and which is redundant?

I could try trial & error but at the best it's a PITA and I don't want to fry anything.

Help mucho appreciated.