demon 340 wont start, no spark

If you have the correct wire, the Brown/ yel (see page 8-147, engine bay) goes from the center pin of the neutral safety switch to one of the two "push on" terminals of the starter relay. This provides a ground to the relay in park and neutral, and allows the relay to function

If this is screwed up you can get the engine to crank with the key by simply temporarily grounding that terminal of the starter relay

This WILL NOT have any effect on a spark problem

Do you have any reason to believe the wiring is hacked up? Evidently you have operated this car previously?

"Old distributor" Is this points or what?

What all is connected to the coil NEG? I would disconnect tach if it is hooked up, and ONLY connect the ignition system, IE the black pertronix wire, and by the way, the coil mounted capacitor / condenser should connect to the coil +. I would ALSO leave that loose for now

Can you provide a link, ETC to the pertronix product? Is this a two wire black / red deal?

If so, black goes to coil NEG, red goes to coil + AND to 12V