It states right on the directions of the pertronix ignitor wiring diagram, below the 3 different coil wiring images,
"Note: A resistor wire or ballast resistor may or may not be included in the original equipment. They are not to be changed in any way with the installation of an ignitor system".
When I used one, I ran it off the factory resistor wire with no problems, and the tic toc tach worked perfectly. I now use a chevy HEI and for that you do have to remove the resistor wire and run a full 12 volts. The tic toc tach lead plugs into the tach connection on the HEI and works fine. The best way to hook the wire up is to unbolt and separate the wiring bulkhead at the firewall, then locate the resistor wire, and take some needle nose pliers and pinch the spade connector, then push it out. That leaves the resistor wire intact if you ever need it later. Then at an electrical supply store or a car swap meet, buy a few spade connectors(to have extra), use some red 14 gauge wire and crimp the spade connector then insert it back into the location of the resistor wire, reconnect everything and clip it to the IGN terminal on the HEI cap. Works like a charm and is reversible if you want to go back to original.
68 RS/SS 350 Convertible<br /><a href="http://img.villagephotos.com/p/2003-9/393973/compressedimage1.JPG" target="_blank">http://img.villagephotos.com/p/2003-9/393973/compressedimage1.JPG</a>