Normally you want to be able to control the lights independently for all of your factory lights since there are circumstances that you wont Want them on...

The best way, IMO, to prevent accidentally leaving them on is to power the switch via an accessory wire leading to the steering column. That way the switch can't get power when the ignition is off.

Three things to consider though;
1) warranty. Tapping into the OEM harness has its obvious concerns if you're still under warranty, should you have any electrical issues directly related to that harness.

2) I would put a fuse there so you don't blow the entire circuits fuse is something shorts. (Hence a 10amp quick burn fuse).

3) I wire my switches from a constant 12v source. I don't like the idea of leaving my keys in the ignition while I'm using the lights and I'm not in the Jeep (say helping someone on the side of the road at night.... then someone could hop in the Jeep And drive off while I'm changing someones tire...)