Background: Previous owner of my 64 Dart converted to Pertronix and uses a Pertronix coil. A four-post ballast resistor remains wired somehow to hide the installation of the Pertronix. Today I am installing a SunPro tach and instructions for one of the wires reads: Connect the wire to any vehicle harness wire which is energized with battery voltage ONLY when the ignition key is in the ON (RUN) POSITION. NOT OFF or ACCESSORIES. How would wire the tach? I already have wired the tach to ground and to the (-) side of the coil.

Find a switched fuse at the fuse box and tap in there using a spade terminal shoved between the fuse and the clip that holds the fuse.

Reed: How about something in the engine compartment instead? My fuse box has some serious issues. Maybe when and if I get one in better condition, I will do what you said.