In the wiring loom it's before the ballast resistor although I don't think it would matter. It works by sensing the current flow through the wire and is not physically connected. I doubt that 6 volts is significantly safer than 12 (after, before). Mine's never actually worked unless it's plugged in right at the coil, not sure why but I'm working on it. It worked a bit when I had the dwell set too long on my electronic ignition and burned out the coil.... Next thing is to try 2 loops (double the strength of the signal to the sensor).