Easy to install, perfect match with the car Allows the addition of 2 or 4-channel amplifiers to most stereo systems without output-allows the addition of amplifiers and subwoofers to existing factory systems The device has a built-in relay. When your stereo sends sound to the speakers, this device converts the speaker signal to the amplifier's jack, and at the same time, it provide you with the voltage required to turn on the amplifier with 12 volts from the amplifier's power supply end. High-level speaker signal to low-level adapter specification: Applicable models: Suitable for most models on the market Colour:Gray Material:ABS Size:5.5x3.5x3cm Package Contents: 1* Audio converter Only the above package content, other products are not included. Note: Light 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.