When I try to start the truck sometimes the starter won't stop spinning. I have to take the battery cable off to stop it. And sometimes it won't do anything when I try to start it and have to jump across the solenoid to start it. I have replaced the solenoid and still the same thing. I thinking a bad ignition switch? Truck is an 88 F150 4x4.

 

You could well be right about the ign switch. It is on top of the steering column under the dash.
However it could also be a problem with the linkage connecting the key switch to the ign switch.
There is a two piece cowl around the steering column right where it meets the dash, take this off (two screws). You will now see the rod that connects the key switch to the ign switch.
Lift a battery terminal off. Put your finger on the rod and then turn the key round to the start position and back to off. The rod should move in "time" with the key. If it does then most likely you have a bad ign switch.
If it does not then most likely the pot metal ign actuator in the column is broken.

 

I going to say it is the solenoid, inside there are points and they will weld together to create a constant supply.

 

Finally go around to looking in to this. The linkage connecting the two seems to work fine. I tried holding it while I turn the key and it moves in both directions. I dropped the steering wheel where I could get to the switch. Is it as simple as unplugging the wiring and removing the two nuts? Anything to watch out for?

 

First off always a good idea to lift off the neg battery terminal then just unplug the ign switch, unbolt it and disconnect it from the rod coming from the key switch and you are done.
When replacing it you may need to leave the two bolts slghtly loose so that you can slide the switch up or down the column a little to get it properly adjusted.