when I try to start my truck (79 F-150 with a 302) it tries to start but won't the only way it stays running is if I hold the ignition button in(truck has a push button to start truck) started fine until yesterday.

 

Check any fuses associated with the PTS. The PTS button should only give hot to starter when you push the button and Ignition hot comes from key ingnition. If the distributor and coil isn't getting continuous hot it will not run.

 

Thanks never even thought about checking the fuse. Hope it's that simple.