stop by a local stereo shop and have them look @ your factory radio. starting about 2007 w/ the wrangler they started to use can-bus wiring for radios.. so may not be a normal $15-$20 wire harness. may need the $130 one. just a little warning. 2008 wrangler radio parts
you probably have the factory Infinity system in the jeep as it is...which makes it alittle more fun to do. since there will be a factory amp in there. sometimes can't just swap stuff w/o changing everything. some of these systems already cross over the factory speakers and aftermarket are made to run more full range.
if you do have the infinity system and a can-bus wiring i would realy look into how much you plan to spend. bc sometimes you may have to replace radio & all speakers as well as re-wire speakers to radio. though sometimes you get lucky and can use factory amp and just replace speakers.
if the only thing your looking to do is add a sub and you like the way jeep sounds then just do that. you can do that to any radio. no rca's on factory radio. only difference on installation from a factory radio compaired to aftermarket are the rca's & amp turn on wire. though u can get a line level converter to change factory speaker wires to rca's make sure you get full range signal or factory sub signal. it's not as clean as a aftermarkt signal but will get the job done..sometimes if you turn off radio you may get a "thumping sound" since amp turn on wire would be hooked up to ign. source and not amp turn on off a aftermarket radio.