Many moons ago had similar problem. Gas tank was sealed with plastic goo which dissolved and wound up in the bottom of float bowl. When going up hills goo moved against main jets, blocking fuel flow.
Suspect it's 12volt lead to coil while cranking engine. With engine running ignition wire goes thru resistor on coil first.
The big ugly cable is from battery positive.
Experiment with headlight switch to determine which terminals to connect to for parking and headlights. Make sure various light fixtures have good ground.