Using a car stereo will give you a front/back fader which you could use for cabin/cockpit speakers; this allows for muting the cockpit
when in harbor so as to not annoy the neighbors. Many car stereos are designed for 4Ω speakers, so it would be possible to parallel two 8Ω speakers for each output. The extra speaker wire might be for a sub-woofer. If it were me I would trace every wire first and locate each speaker, identifying the impedance and power rating for each. Also, keep in mind that + and - needs to observed or one speaker could cancel the sound from another (sort of). Mark every wire with speaker ID and polarity (e.g. Starboard Saloon
+). Then decide how to hook it up. Right now nobody can help with just a bundle of wires, and I wouldn't recommend hooking them up until you had a diagram.
More generally you should make a wiring
diagram for the entire electrical system
: it will save you a lot of time in the future and you will learn the state of things in the bargain. It is not unusual to have hidden electrical
problems so don't just assume all is well. I think most people I have recommended this to have thought it too much work
, but then went on to waste a lot of time troubleshooting every time something was installed or a problem occurred. It is a worthwhile investment.