Ive got a 79 f250 with a 400 in it. When I turn the key to the on position it immediatly starts to crank and I have to physically shut the key off to get the starter to quit cranking. The solenoid looks new and I put a new ingnition in it today thinking that was sticking but it did not work. I havent got the truck running yet, it fires but I have to turn the key off to get the starter to quit so it wont run for more than a few seconds. The key will turn one click the as soon as I start to turn it she starts cranking away and when I let off the key like a normal car it keeps cranking! please help. thanks in advance

 

sounds like your ignition switch is not wired properly, or the wires are shorted somewhere...

 

The key cylinder may be bad. Do you have a remote starter?

 

Sounds like the switch is misaligned.

 

The first thing to check is the wiring at the starter relay(solenoid). You may have the solenoid with the two small connections on top. One is labeled "s" and the other "i". If these two small connections get swapped, then it will act as you describe. If you have a red/blue wire as one of the small ones, connect it to the "s" terminal.

 

I have replaced the key cylinder and the ignition switch? that the cylinder goes to. Still no luck. Yesterday I started swapping wires around on the soleinoid to see if that would help but it didnt. Still turn the key and it just cranks away until I turn the key off. The solenoid looks new but could it be bad? I dont have much experience with older trucks but they seem simple and i think thats why im getting so frustrated. Thanks for the replys everyone

 

1978/1979 F Series uses a DIFFERENT solenoid switch than the earlier 1956/1977 switch.

E7HZ-11450-A Starter Solenoid (Motorcraft SW 1507-B)

Note: Above part number may updated. Use the Motorcraft number in a parts house, they can cross ref the number.

 

That could be a possibility. The truck was not running when I bought it so who knows what the last owner replaced the soleinoid with! I give that a try tomorrow. Thanks

 

That puts a whole new light on the subject. It could be several things. See if you can find the red/blue wire that goes to the solenoid. It does go to the "s" terminal. Get a voltmeter or testlight, and with it disconnected, turn the key to run and see if you have voltage on this wire. This wire should only have voltage when the key is sprung over to start.

If you have voltage, then I would go ahead and pull the ignition switch out. One of the wires on the switch should be the same red/blue. Turn the key to run, and check for voltage on that wire at the key. If you have voltage on it there, then something is wired wrong or there is something wrong with the switch.

This wire leaves the ignition switch, goes to the neutral safety or clutch switch, and then goes right to the starter solenoid connection.