Download Installation CONNECTING THE GM20SR NOTE: Due to the design of the Standard Amplified system, there is currently no way of fading from front to rear with an aftermarket radio. NOTE: If using a SWC-1 (SWC), the green wire on the SWC-1 is connected to the red wire of the red 20-pin harness. SWC-1 must be programmed for Version #1. Step 1. Prewire the GM20SR 18-pin wire harness to the aftermarket stereo wire harness. If the aftermarket stereo has a mute wire, cut the brown wire as close as possible to pin #16 of the GM20SR 18-pin harness and connect this mute output wire to the stereo’s mute wire. The amp remote wire (Blu/Wht) must be connected to the stereo’s remote wire. Connect the 16-pin wire harness to the GM20SR main interface. Step 2. Connect the black 8-pin, brown 8-pin, and the red 20-pin harness to the factory radio harnesses. Connect the 16-pin wire harness into the GM20SR. TESTING AND VERIFYING OPERATION 1. Turn ignition on. The red ignition LED on the side of the interface will turn on and the +12v accessory wire will turn on. 2. Turn on the radio and check the balance. NOTE: Audio will not fade as the rear outputs of aftermarket radio can not be used. 3. Pressing the OnStar® button on the mirror will mute or turn off the radio and allow the audio to be heard from the speakers. The OnStar® active red LED will also turn on. When OnStar® disconnects, the radio will un-mute or turn back on and the OnStar® LED will turn off.