Heavy Pink wire at firewall connector

[65k10]

Searched the forum and found answers to all my wire questions except this one. At the firewall connector, attached to the same terminal as the coil wire (a resistor wire) is a 12 or 10 gauge Pink wire. It is long as if it went to the carb.
It is a Midwest truck so I wouldn't think it would have any Smog controls, but I've been wrong before. It's a 69 GMC 1500 with the 307 and Turbo400. Factory carb was gone when I got it. I haven't seen any diagrams that show the the Pink wire attached to the coil wire terminal at the firewall. There is a smaller pink wire that comes through the firewall next the the connector, and I know that went to a switch on the carb and then went to the kickdown on the 400.

Any help appreciated.