What is the best wire (out of the ignition switch harness) or alternately out of the transmission shift selector (trick truck into thinking it is not in park) to splice a kill switch to?
I have done it before on my MR2, but that one was manual and I just spliced into the clutch switch .

I know car can be taken many other ways, but would just like a way to eliminate the possibility of starting it even if someone has the keys.

 

If you splice a switch into the transmission park wire, you won't be able to get the key out of the ignition if the switch is on (can only remove key if car thinks transmission is in park). That could be okay, just be aware of it.

My first choice would be to find the wireless transceiver for the security chip (in dash near ignition switch), and splice a switch to cut power to the transceiver. The key will still crank the engine but it won't start.