Reverse lights??????

OK so OEM automatic, then later a manual, and now automatic again. No wonder its a little confusing. In 67 automatic the reverse lamp switch was inside the car either on the column or on the floor shifter. That's why you don't have purple wires through bulkhead.
Power is there at switch on but only 1 of the 2 wires, shifter to reverse activates switch ( now on transmission ) = both wires hot, power continues back into the cabin and on to the rear harness.