This is just a WAG, but if the three wires enter a two-cavity connector, it may attach to the two-prong oil pressure switch for the electric choke heater. Factory color coding for that circuit is pink/white, dark blue and light blue with the dark and light blue wires sharing a terminal. Heat and oil soaking over time can cause the light blue insulation to take on a green appearance. If it is for the electric choke and the BB you installed uses an electric choke carburetor, it could benefit you to reuse the circuit. To determine whether it is for the choke heater, with the CHOKE fuse installed in the fuse box, switch ON the ignition and check the pink wire for 12 volts. With ignition still ON, grounding the dark blue wire should cause the choke lamp in the instrument cluster to illuminate.