69 barracuda wiring questions

Doubt whatever diagram you bought was a factory one. Those are in the shop manual.
Both the shop manual and the assembly drawings will be very helpful for what you are doing.
One of our FABO members has made a layered pdf version from the 1969 shop manual. Do a search 1969 Factory wiring pdf and you should be able to find it.
There is only one source for the assembly drawings, and that is the reduced versions in the book sold be Faxon. Discussed here Resto manual

Reverse light wiring for '69 is different than '67, and '68.
The way I'm reading the wiring diagram, for a 4 speed with console, cavities C and Z are connected on the bulkhead. Without console, wire B2 connects between cavity C to the switch, and wire B1 to cavity D.

Maybe tonight I can spend more time on it, but that should get you started.