The ignition switch leads are usually labeled. If not, find the one that supplies power to the coil when the switch is turned to the "run" position. It's going to supply the 12 volts to the pushbutton, relays, etc. If there's a ballast resistor in the system, the power to the pushbutton needs to be connected upstream of the resistor, not at the coil (+) terminal.

Is your HEI system an original-equipment GM or one of the Mickey Mouse aftermarket units? The GM HEI's have a "tach" terminal in the distributor cap right beside the big power input wire. That's the one you would use that would be grounded by the relay in place of the (-) coil terminal. I'd need to see a schematic of a Pertronix circuit to figure out where to ground the trigger signal without burning something out.
Jerry


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