I have an 03 that I put a Nav system part#15204334 via "plug and pray". I had to buy an antenna and the map disc. All I did was take it to a GM dealership to unlock the radio and it works perfect with no mods. Total install was less than 2 hours. Hummer said it couldn't be done
. The 05s' take the newer touch screen Nav units from escalades, and other GM vehicles. The best place to buy the Nav units are on Ebay. Most of them will say what they will fit. The best place to buy the Nav disc is
www.gmnavdisc.com. I got V5 for $199. Hummer in Birmingham wanted to charge me over $400 for v3.
This is my first post so sorry if I sound like an idiot!
