I experienced this exact problem on a '77 280Z. It turned out that under the center console of the '77, there was a ground wire w/a bullet connector on it. This ground had been plugged into a female bullet connector that fed the ashtray light. Hence, the whole parking light system had grounded!!! I'm not sure if a situation like this exists on your '73, but its worth looking for. Also check for bare wires that may be grounding on the body. Places for this may be where the wiring loom passes through the firewall, and along the passenger's side rocker panel, etc. If that doesn't do it, start at the switch and work your way through the system from there. Good luck...
Ian
> Whenever I turn on the parking lights, the
> fuse blows. I disconnected all the parking
> lights, and it still does it, so I'm
> assuming there is a short somewhere in the
> wiring. Any suggestions on where/how to
> start?