I used the basic harness, I did not lose my chime functions but mine still come from the dash and not my speakers. I believe certain GM SUV's from 2003+ with the RDS radio's require the expensive adapter because the chime feature is run through the stereo and outputs from the driver side door speaker or dash speaker, from what I have read. If your chimes still work then I would not worry about it.

 

I'm not sure what harness it was. It was for 04 model year though and the orange illum wire or speed sensor wire is the only one I didn't hook up.