Will a Wrx/sti stock head unit from a '08-'12 fit directly into a '05 sti. I've always wanted to go after market for aux input but wanted to keep everything stock inside.. I can get a used (non- nav ) HU on eBay in the $70 range. I've seen the regular '08-'12 HU's with the aux button on the face. So will it be that simple to just buy an aux cord along with the HU?
I know some of them have the harness that goes down towards the ashtray area. So even if I used an '07 HU it wouldn't work? Center consol is same. Seems like it would be a direct fit?
Short answer: Yes, a 2007 HU will fit your 2005, and the power/speaker harness will be plug-and-play.
Huh? What OEM HU model number do you have? According to cars101.com, the OEM non-nav HU in all 2011 WRX/STi models includes aux (and USB) capability -- all trims got the HU model CZ624U1 (printed on the face). And the optional nav HU in that year includes aux (just doesn't have a hard button labeled "aux"). In some 2008-2010 models, the HU had an aux button, but the 3.5mm jack (in the armrest console) and its harness were an optional accessory. ADDED: I later realized Doonamis said "on the face". No Subaru HU has had that (a 3.5mm aux jack on the face of the HU itself) in more than 10 years. However, all of Subaru's OEM HUs have had a rear aux input (via a proprietary socket) since model year 2007. But many lower-trim models shipped without the actual 3.5mm aux socket in the armrest center console (and that was usually available as an accessory from a dealer's parts dept.).