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 to 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 the optical fiber signal of the device, (common For example: 6-disc CD, telephonecommunication (Optional) Optical Fiber Audio Decoding Box Name: Optical Fiber Audio Decoding Box Compatible with the following models: for E-Class W211 (2005-2008), for S-Class W220 (2004-2006), for SL-Class W129 (2005-2008), for W219 (2005-2008), for W215 (2004-2006), for W171 (2005-2008, no SD card slot). These for models are not suitable for installation on models equipped with audio systems. Please check as much as possible to the item is what you need. Color: As Shown Material: plastic Package Contents: 1 * Audio decoding converter box 1 * Fiber Optic Shorting 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.