I just happen to have a 73 Dodge service manual here on my coffee table. If that wire is considered DBL (dark blue) as opposed to LBL (light blue), that color runs rampant through a splice to various things. Rear window heater switch, electric choke, ballast resistor, dash pcb and ignition switch for instance.
But because this problem seems to be hidden, how about the seat belt system? It seems to me that the seat belt interlock stuff started sbout that time. A lot of people were annoyed by the whole thing and it was common to bypass it. I see DBL wires going to a seat belt relay, warning lamp, buzzer, seat belt retractor switches. Maybe there's something there?
