1. The HFS is *not* a standalone device. It must be used with a vehicle specific harness (sold separately). The following will help determine when the HFS is OR is *not* required: 1. If connecting to a vehicle using a PPH _ _ _ _ (i.e. PPH1858, PPH1721 etc) harness, the HFS IS REQUIRED to complete the installation. 2. If connecting to a vehicle using a PX _ _ HF_ (i.e. PXVWHF2, PXFDHF etc) harness, The HFS is *NOT* required to complete the installation. 3. If connecting to a vehicle using a _ _ CSS _ (i.e. GMCSS2, FCSS1 etc) harness, a MOT-1000, PT-3100, PT-3200 or UPA-2 sub-harness is required to complete the installation. (The HFS is *not* required). 4. GM OnStar is not a Bluetooth system, therefore you will not be able to use GM OnStar equipment (microphone etc) with an aftermarket Bluetooth Kit. You must use the microphone included with the aftermarket Bluetooth Car Kit (i.e. Motorola IHF1000, T605, Parrot etc.).