John is correct.

The "remote" lead off an AMP is for the remote POWER on/off. It senses when the HU turns on and let's the amp power up. It should always be connected to the "remote" output on the back of the radio. If no "remote" lead available on the HU, you should probably connect it to the switched power lead that powers the radio that way it gets power at the same time the radio does. You don't want to hook it up to a constant power source.