demon 340 wont start, no spark

the car was originally 6 cyl. with a/c. It ran before I tore it down. it has the electronic distributor system. I called laysons restoration in Tacoma & was told the brown/yellow wire that is on my car and goes into the firewall, not over to the relay, has to do with the reverse lights. the tech I talked with got the info. from a 73 dart wiring diagram. my old harness had the wire attached to a blue/white wire in the eng. harness going to the relay. it looks all stock, but I can't find a match in my manual. i did run a wire directly from the battery to the coil & still no spark. thanks for the help.