Run Stand

I used this set up on my race car to bypass my older MSD 6200 box that I suspected was bad. It appears it was bad. I used a jumper wire from my big relay(forgot the part # it looks like a Ford solenoid) that I use as a 12 volt source for everything in the engine compartment. When I turned the ign switch off, the engine ran for about 3 seconds before it stopped running. I'm assuming it was some feedback from the alternator. If I used this system permanently could I use a Bosch type relay to switch the 12 volt to the ign coil?