Axxess Metra GMOS-04 Adapter Harness Description:GM amplifier interface harness. Retains chimes and accessory. Works with or without OnStar and provides navigation wires. Product Specifications:-For amplified audio systems; Premium and Bose-Retains OnStar with adjustable volume output-Retains chimes with adjustable level output-Retains RAP feature-Navigation outputs now included-USB update interface compatible The GMOS-04 interface is designed to allow the user to replace the OEM radio with an aftermarket unit in amplified GM vehicles and retain full functionality of the OnStar system as well as all safety and warning chimes. The GMOS-04 will also retain the retained accessory power convenience features. This interface has the capability of adjusting chime and OnStar volumes as well. In addition to these features, the GMOS-04 now has the required outputs for the installation of a navigation radio.