Fangrui Product Details 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 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). Installation Location: Behind The Car Audio Screen Host, Or Behind The Car Amplifier. Function: Convert External 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 Exam