neutral safety switch.

Yep, odd as it may seem, this single brown wire was pretty much just tossed in along beside the taped harnesses for automatic trans builds. Mid 1968 the reverse lamp switch from automatic builds moved out of the cabin and down to trans, like the manual trans builds. Those 2 wires went out through previously unused ports of wiper motor connector of bulkhead. The brown wire from starter relay joined those to become a 3 wire harness to a 3 post dual function switch.