Wild wild wild ... Back in 67, the reverse lamps weren't fused. If owner backed over a tricycle and and damaged a reverse lamp fixture just right, it would blow the main fusible link and shut down the entire car. So the 68 model harness has a white wire going from radios harness connector to bulkhead connector, only for a place for this wire to change colors again and be on a fused circuit. There isn't a wire in the engine bay at this port. So radio and reverse were on the same fuse. When I was helping a owner with his 72 model wiring, the wire added to radios harness connector changed colors at the bulkhead and went to signal flasher instead of reverse lamp switch. Best I can figure, they moved stuff around, did low dollar improvements until they had no choice but upgrade a harness with multiple fusible links and more fuses. Some of the vehicle could fail in accident but some of it would still work.
