1984 f-150 won't stay cranked
 

my truck will run as long as starter is engaged. as soon as i let off key...into "run" position, it goes dead. i have replaced solenoid, pick-up coil in distributor, new ignition control module(5x5 box on firewall), new plugs, new wires, new timing chain, new ignition switch, new key tumbler and i am frustrated. any suggestions?

Some basics- we need fuel and spark.
Could you provide us with;
Engine size and the 8th digit of the vin # please?
Do you know for sure if you have spark available at the spark plugs?
To better assist you, do you have a test light / voltmeter available to use?
I believe the engine has a carburetor and is not fuel injected , is this correct?