Car cd player connection tail line is one of the most basic work of car audio modification maintenance workers, if the original car audio is replaced, you can realize identification through the original car tail line, the corresponding wiring can be done, when there is no original car audio, by using a multimeter to measure out the tail line use, the original car has no audio need to be installed, you can take electricity from the vehicle battery, install an insurance box, The positive pole is connected to the 12V negative pole, the Acc is under the steering wheel, and the horn line can be laid.