Once you get the old marine stereo out, it's time to put the replacement in. If you are replacing your old stereo with one that is the same brand, you are in luck! It is very likely that you can use the old wiring harness and just plug it into the back of your new stereo.
If your new stereo is not the same brand, you will probably have to splice some wires. You will need to cut out the old harness and splice in the new one. It looks intimidating, but it isn't as bad as it seems. The wires are color coded to help you out. You can often just match up the colors as you go.
If the colors on the old harness don't match the new one, here is an instance where an installation manual for your old stereo would come in handy. In fact, if you can't find the exact manual for your old stereo, a manual for a similar model of the same brand will usually do the trick because manufacturers stick to their color coding. Just look up the wiring diagram. Your new stereo will also have a wiring diagram in the manual so you can match up the wires.
Eight of the wires on the harness are speaker wires. Most stereos will power four speakers and each speaker needs a positive and negative wire. That eliminates most of the wires on the harness. The wires left all have to do with powering the unit. Although colors may vary, this is how they are usually set up: The black one is the ground wire. Ultimately the ground wire connects to the negative terminal on your battery. The yellow one is the positive power wire and it connects to the positive terminal on your battery. The red one is a switched power wire. Typically the switched power wire connects to the boat's ignition so that when you turn the boat off the stereo will turn off. This wire must be connected to power in order for the stereo to work, so it is essential that it gets connected. The blue wire is a control wire. If you are using an amplifier or some other kind of external device that requires power, this connects with the switched wire on that device. That way, when you turn off the stereo, the amplifier will turn off with it. Connecting the blue wire is completely optional. After all the wire connections are made, it is time to plug it into the back of your new stereo.
The back of the stereo is usually supported behind the dash with a bendable metal strap. There is a bolt on the back of the chassis. Push this through the hole in the strap and then twist on the nut to fix it in place.
The front of the stereo can be attached to the dash in several ways. You will either use screws or a mounting sleeve. Your new stereo will come with clear instructions on how to do it. Since many models are different, we recommend following the instructions in the manual to finish off your installation.