OK, Izzy, here's an "ideal" scenario for retrofitting such a system. You can pick the eyes out of it for other situations.
Start at one of the main "splices" in your underdash harness. They may not be visible and hence need to be unpicked in the tape wrap to access. Check your wiring diagram. Using fresh soft solder (electronic type with high silver content), piggyback your new over-rated ignition feed wire to the main line in. The Teflon type coated wires are nice and durable for engine bay work, but try for an appropriate or original colour.
Now hook this feed wire to a discreetly placed kill switch. Again, solder all connections to maximise current flow. Cover exposed bits with heatshrink or tape. Now, tape (strap) the outfeed of the kill switch to the old harness, and run it out through into the engine bay. Sometimes, it may be easier to push it through another grommet for choke or heater hoses - your situation will define this.
Either way, head for the coil positive. Mount your resistor(s) in a shock/vibration minimised place; not on the motor. Be sure you can always see them to check up. Use spade connectors to join this wire end to the resistive mass, but solder the connector once again and heatshrink. A "piggyback" connector on the resistor is where you take off the 12V for the Pertronix. The far side of the resistive bloc goes to the coil.
Always check both your coil and the distributor body (and breaker plate) for perfect grounding with a meter.
Cheers, Adam.
