Originally Posted by stockcar nut
My condolences to you, I am having the exact same problem with my 77 F150. It only tries to start when you let off the key. Never mind the key switch, I replaced it this morning to no avail, ditto on the coil. I am down to the module or the dizzy, but I know it has to be in the starting circit between the key switch and the dizzy. I am not sure but I dont think there is a relay other than the solinoid. Does anyone know if you can jumper from the battery to the hot side of the coil to start one?
Your starter solenoid should have two small screws sticking out of it, one is "S" and the other is "I". The one with the "I" has a brown wire going to the Ignition Coil. This wire is off, open or you have a bad solenoid.
If you do not have the two screws then you will have to replace the solenoid with one that does.