Do you have your originals to reference?
Wiring diagram in the back of your '67 Ford Mustang shop manual will help to sort all back there Mustang related.
OK, I'll try this, there are the two pig tails for the back-up lights, should have molded two-wire male/female ends.
There should be a single male end for the license plate light.
A tail light ground wire that will ground/attach on the right side (passenger) of the fuel filler neck/center sheet metal with star washer (cut the paint) and self-tapping metal screw, see attached image.
A two wire set black and green - left side feed to (Mustang) tail light and another longer set has to run across the very rear of the car and held up by the metal tabs up under the rear lip, black and a orang-ish right side feed to (Mustang) tail lights. Seems yours maybe green/red stripe and black and red-ish.
The tail light left and right pairs connect to your two tail light 3-socket pig tails with the off-white scotch-lok connectors.
Also, there were 3 versions of how the 3-socket pig tails were handled; loose wires = early, wrapped with black tape or inside black tubing/sheathing. Typically if the second or third version it would match what was done for the amp wire gauge wires in the engine compartment.
Will add some images that may help, have to locate them...