So here's my idea, he has a manual truck and coming up with a kill switch that is really hard to find and is not a liability to the truck while it's running is the goal.
It's an 88, not sure if it's a distributor or just and ignition module but here goes.
With a manual, just disabling the starter coil won't work as the truck can still be push started. So I am thinking of tracking down part of the ignition system, the power to the ignition coil maybe? Interrupt that circuit, install a suitably amped relay and run a wire into the cab for a switch? Ideas? has to be something that is A: Not easy to see and B: Not quick and easy to bypass.
With the switch my original idea with an automatic and interrupting the starter coil is to install a magnetic switch in the center console on my 2nd gen underneath the coin tray. In order to start the truck you would have to put a magnet in the coin tray to close the circuit on the switch. Problem is that he has a manual and that won't work. The other problem is that if you interrupt the ignition coil, the magnet must stay in place for the truck to run and the coin tray idea doesn't sound like the best way to do this. It would have to be something where the magnet is held in place until you pull it out. IDK, a discreet slot of some kind? Something, either way, the idea is that it would be a switch but not the type of switch a thief might look for and if the switch itself is mounted in a fairly inaccessible place then it will be pretty hard to find with out tearing the dash apart which won't happen because who in hell would think of looking for a magnetic switch, mounted under the speedo bezel that is tapped into the ignition circuit? I'm thinking that if a thief can't get the truck started under a minute or two tops, he's walking away.