There are two different ways you can get a signal into the CE404 - low and high level input. A low level input is measured in voltages. It comes in the form of RCA outputs from the back of your receiver and goes to the RCA inputs on your amplifier. A high level input is measure in wattage. It comes in the form one positive and one negative wire from the back of your receiver, and goes to the input terminal of your amplifier in the same wire form. Low-level (RCA) input wiring is preferred for best audio performance. Always use a high-quality RCA cable for best audio performance. Note: do not connect both the high level and low level inputs from your receiver to your amplifier at the same time.
Properly setting the gain on your amplifier is key to getting great sound in your car. The gain control is not for adjusting volume, it simply adjusts the amount of signal that is coming from your receiver and going to your amplifier. If you set it too high, you are introducing distortion into the sound. But if you set it too low, then you are choking back on what the amplifier is there to do in the first place. A technique that works on most amplifiers involves first turning the amplifier’s gain all the way down. Then, go up front and put on some music. Now crank the stereo's volume until you hear distortion, then back it off until the distortion goes away. Go to your amplifier and turn the gain up until the distortion comes back. Last, back off until the distortion goes away.
This simply shows you if the amplifier is on or off.