One wire goes to the coil and the other wire goes to a switched 12V source. On mine, I wired that one directly to the ignition switch. One of the wires on back of the switch feeds to a fat pink resistor wire via bullet connectors. I made a Y adapter out of bullet plugs to tap into this junction, then ran the new wire through the firewall grommet and along the engine harness to the Pertronix. Worked great.
Apparently, in many cases the pertonix will work fine if you just wire both wires to the coil. This has been debated on VMF. Because the coil is a 6V source, my understanding is that weak wiring in a 35 year old car can potentially cause Pertronix problems due to undervoltage.
Whisperer has an excellent site on proper wiring of a Pertronix. If he doesn't respond to your post, you may want to send him a message.
DanM
66 Coupe, check her out at
http://www.66CoupeNW.stangnet.com
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