Wiring pendant lamp

I have a new socket for a 175 watt MH pendant lamp but am not certain
how to wire it. The ground wire is a gimme, but do I hook the white
(hot) wire up to the spring that touches the center "electrode" of the
bulb or to the threaded part of the socket that the bulb screws
into? (I'd just look at the old one, but I don't have it in one
piece anymore, sad to say.)

Thanks!

Rancho