The one wire going to the bulb socket is blue. The other green wire was cut. Where does that green wire go ? Is it a ground ? Most of the other bulb sockets have red with blue stripe wires, but mine is blue. I don't see a blue wire on the wiring diagrams going to the bulb sockets either. Thank you.

It's not a stock socket. Stock sockets in the 240Z are grounded to the gauges, IIRC. The green wire on that socket should be your ground.