I have the standard HU, can I just swap in the mp3 version (direct plug in) or is there more to it

 

In my '04 Lariat, the CD-6 MP3 head unit plugged right up to the stock harness to replace the original single disc CD player/AM-FM radio. My steering wheel controls don't exactly work the same anymore though; with the single disc CD unit, the "SEEK" button would scan through my presets, with the CD-6 unit, it scans through all frequencies now, disregarding my presents.

Hope that helps.