Function: Convert external audio signal to optical fiber signal, and transmit to the car amplifier through optical fiber. The sound came from the sound of the car. Special attention: when you connect the cable, If the sound is abnormal. Please note that this phenomenon is not a problem with our fiber conversion module. This is the vehicle's fiber communication system cannot communicate normally. If there is no sound after installing the fiber optic box,Pls check it as following steps: 1. Confirm whether the power supply is connected well, measure with a multimeter, yellow --- battery power 12V, black --- ground wire, no need to connect ACC power supply 2. Confirm whether the gateway signal is connected well, CAN-H, CAN-L 3. In the optical fiber communication of the vehicle, all the optical fiber signals must be ableto communicate normally. Due to the damage of certain electrical equipment of the vehicle, the optical fiber communication is abnormal. At this time, it is necessary to short-circuit theoptical fiber signal of the damaged device, (common For example: 6-disc CD, telephonecommunication module, or directly install the optical fiber audio box to the caramplifier) 4. The W211 power amplifier is located on the left side of the car's trunk, above theleft rear tire, and the W171 power amplifier is placed under in front of the car's co-driver Name:Optical Fiber Audio Decoding Box Working voltage:12V Applicable models: For : E series W211 2005-2008 S series W220 2004-2006 SL series W129 2005-2008 series W219 2005-2008 series W215 2004-2006 series W171 2005-2008 without SD card slot Colour:As Shown Material:plastic Package Contents: 1 x Optical Fiber Decoder Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.