First, look to the right of the steering column, if the truck has factory keyless, you should see a box there, with one long screw holding it in from the bottom. It has two connectors on it. Take it down, and that's where you can tag the lock and unlock. Unlock needs to be relay isolated, but lock will take a straight positive. The reason for the two relays is that most alarms output lock and unlock as a negative output.
You need to cut and apply on the Unlock, and just tag lock. I usually use a 451M on these.