ignition switch, whats wrong

ok my car is a 69 dart had a universal ignition switch with bunch of wires hooked up to the ignition plug, so i purchased a reproduction switch looks just like original, plug right in to the ignition plug. new switch has same operating has accessories, off, on, start. NOW THIS IS WHATS WRONG CAR STARTS BUT ONCE IT GOES BACK TO THE ON OR RUN POSITION IT TURNS OFF. PLEASE HELP. CAR HAS A NEW STARTER RELAY AND BATTERY. OH AND ONCE A 6 CYL AND NOW V8. THANKS FOR YOUR ADVICE