Hi I used to have a Ford explorer and I just sold it and got a 05 Chevy Trailblazer Lt. I stripped everything out of it and I plan to put it in my Trailblazer. Wiring everything in my explorer was a breeze,now I have to figure out this Trailblazers stuff. It has onstar and bose system. First thing I need to know if anyone can help me out. Do I absolutley need the $110 wiring harness? or can I get by with the $20 one? some guy was telling me that if I didnt get the expensive one that all check engine lights would turn on and stuff. Also the other question was about runninng the power wire. Am I going to have to drill a hole thru the firewall? I cannot see a good sized hole in it. If there are any Trailblazer owners please help me out. Thanks.