Ballast resistor

I put the old ECU, ballast and finally the old coil in. The old coil worked and it fired right up. I then put the newer coil back in and it fired up. THE ONLY THING I CAN THINK OF IS THE COIL PLUG WIRE WAS NOT MAKING CONTACT IN THE COIL OR ONE OF THE TERMINAL POST WIRES WASN'T MAKING GOOD CONTACT???