Transcript: A Marine stereo doesn't just plug into a wall, like a boom box. Every new stereo comes with what is called a wiring harness like this.
This end plugs into the back of the stereo. These wires all need to be connected to the boat's systems. The harness makes it easier to splice all the wires without the stereo connected and getting in your way.
I know all these wires look intimidating, but it really isn't as complicated as it seems. 8 of these are speaker wires. You can connect 4 marine speakers and each speaker needs 2 wires. So that eliminates more than half the wires right there.
Of the remaining wires, 2 of them are power wires. One is a direct power wire that connects directly to the positive terminal on the boat's battery. The other is a switched power wire. Usually it connects to the boat's ignition so that when you turn the boat off, the stereo goes off as well. If you connect the switched power directly to the positive terminal on the battery, your stereo will still work, but it will only turn off if you push the off button on the stereo. Both power wires need to be connected for your stereo to work. There is also a ground wire that connects directly to the negative terminal on your battery.
Some stereos also have another power wire that is used to control external components, like an amplifier. Connecting this wire to the appropriate wire on an amplifier will turn the amplifier on and off as you turn the stereo on and off.
All wiring harnesses are similar to this, but each manufacturer uses a different style of plug. So if you are replacing a stereo with a different brand, you will likely have to cut out the old harness and splice in the new one. However, if you are using the same brand of stereo you can often just plug the old harness into the new stereo.
The wires are all color coded and each stereo comes with a wiring diagram to show you which wire goes where.