Turn the key on and tap the white wire on the MSD box to ground kinda like doing morse code. Have the coil wire off the cap and close to a ground. If it sparks the MSD is ok if not the box is dead. You can also take the twin leads to the dist lose and quickly tap them together at the box and try that too, either/or will test the box. Make certain you have voltage going to the coil and box before you do that test.