I ran a wire from my coil to a switch to ground on one of my cars. Worked great and simple. Hide the switch where ever you want.

 

I had a 1970 Camaro where the ignition switch was so worn out, you could start it with a popsicle stick. I wired in a two way switch, (single pole, double throw), inline with the neutral safety switch (because that wire was really close to the console where I hid the switch under the ashtray). The other side of the switch went to a cheap 12volt red flashing LED I got at Radio Shack for $5. With the switch engauged, it interrupted the starter circuit and made the red LED flash so it looked like I had an alarm. The switch flipped the other way turned off the LED and allowed the car to start. This would not work if you tired to use the coil circuit, because it used the positive side of the neutral safety switch to power the LED. Having the LED wired in helped my wife remember to turn off the kill switch.