Reverse switch?

I dont know what year model service manual you are looking at or what year the reverse lamp switch moved out of the cabin. What year model transmission makes a difference too. Bottom line either way was possible. If your reverse lamps work they are wired up correctly. There would and should be a single brown wire routed from your starter relay to that single post neutral safety switch.
My guess is you will find that post on your starter relay routed directly to ground.
If your starter relay has the yellow wire only and no whaere to attach the brown wire then you have a relay for a manual transmission car.
I hope all this makes some sense.