Part of the ignition system, it is a small black square...near the intake (by the turbo) and distributer - AKA the right side of the motor. I've never messed w/ SRs personally, but went with someone (Cole or Dan) looking for an igniter chip. You can use something from autozone, but they're like 100-150 new. You can order an actual SR one offline at places. Check out some 240 forums, like zilvia.net or nico.com or someplace big and search "igniter chip" it's a common replacement issue.

 

You can get one from a junkyard out of a 300zx Z32, but if you do you also need the connectors and about 2" of wire on both ends to conect it. For the wiring for the ignitor from the 300zx go to heavythrottle dot com to find it.