I have a 1988 f-250 4wd. It has a 460. When I start the truck the key will not turn it back off. When I connect the battery cables the dash lights up like I had turned the key. The key doesn't need to be in it. I tried changing the ignition cylinder. And the new one was the same way. What do I need to check?

 

The key does turn it on

 

The ignition cylinder pushes a bar running down the column which activates the switch. The bar often breaks.

 

This would still let me start it. Where can you buy one.

 

How can you check if that is the problem?

 

Take off the steering wheel. You need an ordinary bolt-grip puller. Then remove whatever screws you see and take off the collar and the turn signal switch. That should be enough to see if something is broken. I've never replaced this part myself though, so I'm not sure how much further you would need to disassemble.

 

How do you change the ignition actuator on a 1988 Ford F250? - Yahoo! Answers

 

to check to see if it is the ignition actuator, reach under the column and find the little rod that goes down to the ignition switch.
see if you can shut the engine off by moving the rod.
if you can, the actuator is definitly broken.
it only costs about $13 from the ford dealer.