Normally closed momentary switch.

[moorecomp]

Man, I gotta tell ya, on my ZX2, I tried cutting the cam position sensor (did not work), crank position sensor (did not work), ignition (worked - but the unburnt fuel going into the catalytic converter caused a check engine light due to the O2 levels being wacked out), finally I tried the same method you did. Works like a champ. And when I bump start, it starts faster than if I used the starter. I have had this on my car for going on a year now and use it a lot (30-40 times a day). I get no check engine lights (other than the normal ones that go out after the engine restarts). I was just posting about this on another thread. Check this post for insight into my install.

http://ecomodder.com/forum/122284-post213.html

Works for me!

[CoastRider]

without researching anything I just added a push pull sw into the ignition circuit, same as turning the key off. No check engine lights and smooth instant restarts, however sometimes during the restart it idles very high for a few seconds.
Reading what others have done makes me wonder if I should cut fuel rather than spark.

Vehicle is an 1989 F150 4.9 5 spd.