5-pin vrs 4-pin electronic module

My son has a 78 Dodge Motorhome with a 440 in it, it quite running, he took off the ignition module and has the 5 pin, assuming it's got the ecu for being a 1978. He tried using the 4 pin electronic ignition module and it does not work. Could that be the problem he needs the 5 pin, thanks for your help.