Not sure if this is in right spot. But my truck is having some issues. When I turn key it tries to turn over(it's cold) but when I stop and pull key out it continues trying to turn over. Well it continued until battery died. Now when I hook up jumper cables it immediately starts trying to turn over and the horn goes off and lights start flashing.

I am completely illiterate when it comes to vehicles but I'm guessing starter selinoid. What else could it be or have other suggestions?

 

That or the key switch mechanism is bad.

 

There is a single wire with a plastic connector located on the passenger side near the vacuum pump. Disconnect this wire and see what happens when you try to start it. If it still cranks it is probably a stuck solenoid. If it doesn't take a look at your ignition switch.