Stray Connector help

Ok, I dug around in my parts stash and found the engine harness off that old '75 that I saved before it was parted out.

There are 3 boxes on the passenger inner fender- voltage regulator at the front, then likely the speed switch and then another unknown box on the firewall.

The harness that serves all three starts at the firewall box with a 3-wire connector. It then runs forward to the speed switch box with another 3-wire connector. Then goes by the voltage regulator, over to the alternator and back along the engine to the large black connector that is near the firewall, over the valve cover

On my V8 harness I found the plug you are looking for sticking out of the harness about 3 inches behind the large connector. It was a black wire. In your picture above, follow that large harness around from beside the valve cover to along the firewall. I bet you find that single connector there somewhere.

You haven't said whether any of this stuff I mention is even there. If it isn't there's no point in worrying about the wire from the throttle solenoid.