For GM vehicles that have On-Star, you need interfaces...not just a harness. This is because On-Star and all the warning chimes also utilizes the speakers. So simply adding a harness will not allow those features to function. So you will need the interfaces to allows everything to work. GMOS (Axxess/Metra) interfaces range from $60 and up based on which one it is. The most expensive one I have is $95 for the GMOS-01.






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