1972 Ford F-150 Electrical Ignition

We put our '69 Ford F-100 360 V8 engine in the body of a '72 Ford F-100. (We took out the 302 V8 in the '72) Well we cant figure out why it wont crank over, except when we cross the "I" and "S" wires on the Starter Relay or Silinoid. But when we switch the wires it turns startes to turn over as soon as you turn the ignition key to "on". When we put the wires on the silinoid like they are supposed to be and then turn the igition swith to "on" the lights come on and we have power to the coil but when we turn the key to crank it nothing happens. We've replaced the ignitions key and switch with a new one and have replaced the silinoid with a new one too. We have checked the ignition coil and it sends spark to the distributer cap. We are so frustrated we cant figure it out. PLEASE HELP!