I have a 66 and looking at my shop manual schematics, I see some slight differences in the wiring between 67 and my 66. In both cases, the voltage for tail lights comes from terminal "B" on the headlamp switch. On my 66, it's a black wire, designated L-7 on the schematic and wire table. That wire goes to the connector for "body wiring". The other side of that connector it's still a black wire designated L-7.
I have a hard time seeing the numbers on the posted schematic when I zoom into it, but it appears that L-7 is the same wire designation for taillights inn both a 66 & 67.
That wire goes to a "common point " which is what they called a "welded joint" that joins (splices), then fans out to the sockets for each of the six tail lamps to supply + 12 V to the "tail light" filament of all 6 dual filament tail lamp bulbs. In the case of your 67 schematic, there is a "resistance" wire just prior to that common feed point in the path of wire L-7. Speedbird is correct.. Check your license plate light, as it's fed voltage prior to the resistance wire. if it works, your problem must be the "resistance wire" which is in the bundle of wiring between dash and trunk area. Not sure, but I believe that "Body Wiring" connector is in rear trunk area. Bad wire, bad connector pin/crimp or bad resistance wire, can't see what else it could possibly be if license plate light works.
