Aaron,
Ed's given you a bum steer there. Probably all his playing with Fords lately
Was your car originally fitted with amber indicators? If so, the wiring diagram in the workshop manual won't suit your car, and you'll need the FB utility/van version instead. Comparing these two shows you exactly what's what. Basically, the set-up that makes the dual purpose blinker/brake lights work is also what makes the dual purpose blinker/reversing light function.
This has been discussed recently, in
this thread, which includes the FB wiring diagram.
cheers
RET