[droopsnoot]

As I read the wiring diagram, you seem to be correct, the reversing light wire is sw/bl, which is black / blue.

First things first, with the ignition on, do you get a voltage on that wire when you put the car into reverse? And do you then get a voltage on the far end of your red wire, connected via nasty, nasty Scotchlok connector?

The earth wire is brown, but you should be able to connect that at the front of the car as it all goes to the same place.

 

[droopsnoot]

when you say the earth goes to the same place what do you mean?

The bodyshell is the common earth point, most things earth to that. Lots of things earth to it from their fasteners, so you might not see a separate earth wire for everything. The idea is to save wiring - connect every earth point to the shell, and you only need to run positive wires around the place. (ETA - that applies to the 12v supply, not to negative speaker wires or the like).