There is a micro switch with a roller tip on it on the shift bracket where the two shift cables are attached. That switch is supose to kill the ignition for a split second when shifting OUT of ( forward or reverse) gear, ONLY not when shifting into gear.
If the V notch is not activating the switch or the switch is bad then that is your issue.
If the switch is not being activated you can bend the arm of the switch a small amount to cause the V notch to activate it but not to much.
To check to see if the switch is working, start engine and push the roller/arm in to make the switch and the engine should stall. If it does not you need a new switch or the wiring is broken or wrong.