If there is no sound after the fiber optic box is installed, please check as follows: 1. Confirm whether the power supply is connected well, use a multimeter to measure, 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 vehicle optical fiber communication, all optical fiber signals must be able to communicate normally. Due to damage to some electrical equipment in the vehicle, fiber optic communication was abnormal. At this time, the optical fiber signal of the damaged device needs to be short-circuited (common examples include: 6-disc CD, telephone communication module, or directly installing the optical fiber audio box to the car amplifier). Name: Optical fiber audio decoder box Working voltage: 12V Applicable models: for Mercedes-Benz 2000-2003 S/CL-Class 2000-2002 E-Class 2003-2004 SL 2001-2004 C/CLK For 2000-2005 ML Installation location: behind the car audio screen host, or behind the car amplifier. Function: Convert external RCA audio signal to optical fiber signal, and transmit it to the car amplifier through optical fiber. The sound came from the sound of a car. For example: for Mercedes-Benz E-Class Harman Kardon audio system, when the car screen host needs to be replaced, it can be canceled in order to retain the car power amplifier. Material: plastic colour: blue Package Contents: 1 x Car D2B Digital Data Fiber Optic Decode 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.