On a carb truck with electric fuel pump, I think a pump kill is about the best. Like y'all mentioned, they get in, start it up, drive away, and when the bowls run dry, the old truck just stalls out and won't fire up again. Hopefully in the middle of the street, where there's too much attention to mess with it.
On an EFI truck, I'm wondering about a time delay relay on the fuel pump signal from the ECM. It runs the pump 2 seconds at key on, then drops off. A delay timer can get that 2 second signal and convert it to a 45 second signal. Then put the kill switch on the circuit that goes through the oil pressure switch, so that it never comes on to power the pump. Same thing as the fuel bowls running dry, it gets down the road a bit and stalls out.
I don't have this one nailed down yet, but I've often wondered about running a second starter wire that only feeds 6 volts to crank it over (and kill the fuel or ignition as well). It would only work on a crappier looking truck like mine. They hop in, crank it over, and just get the "rawrr rawrr raaaawwwwr rr gh" effect. If it cranks but doesn't fire because its an old truck, there's a good chance they will keep trying so it will eventually catch, but give up when it takes too long. Somebody with a plan to tow it wont be stopped, but it would eliminate all the joyriding kids.
