This is an easy thing to do. The ASD relay is inside the Power Distribution Center on the passenger-side fender well, directly in front of the battery. Unbolt it so you can get to the wiring underneath it that leads to the ASD relay.
There is a dark blue wire with a yellow tracer in it that connects the ASD relay to the PCM (computer). Cut that wire several inches away from where it connects to the relay mounting base. Give yourself enough wire length to work with. Very carefully splice a pair of wires to the two cut ends of that wire. Be sure to use good splicing technique, I would solder the connections and slide heat-shrink tubing over the splices. Do a good job here, take your time as this is not where you want to do a bad job... this is a critical circuit for the Jeep. If you botch it up the Jeep won't start.
Run that pair of wires to wherever you want the defeat switch to be located, in a hidden area is my suggestion. Then connect a good quality SPST (on-off) switch to those two wires. Don't use a small cheap switch that might fall apart, use a good heavy-duty switch since you really want all of this to be ultra-reliable. Mount the switch and you're done.
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