I have looked into four ways of doing this.
The first is to add a battery cut of switch that uses a key like this.
Install this in the starter cable and the thing is not going to start unless they jump it. The install loction would be up to you (the fender, bumper, cab floor, etc).
Second, is to install a relay that uses a wireless transmitter like this from master lock
. Here another one that uses you cig. lighter
Cigar Immobilizer Manufacturer.
Third, Summit racing sells or sold a device that lets the thief start the truck lets go about 20 feet I think it was. Then it shut the truck down, that in turn becomes grand theft auto.
Forth, is to install a Stancor relay (200 amp cont. use) in the starter wire, run a wire from it to a 10amp relay hooked up to a hidden switch. The hidden switch then powers the 10 amp relay only when the key is on and the switch is closed. Then Stancor relay then closes its contacts and then all that you have to do is turn the key.