Boat speaker wiring puzzle

CHARGER2

Petty Officer 3rd Class
Joined
Jun 14, 2012
Messages
80
I am trying to wire a new car stereo to my boat (Alpine stereo, 1990 Mariah bow rider). When I pulled the old stereo out, I looked at the wiring harness and it only has 8 wires (+,-, and 6 speaker wires). The odd thing is there are only 6 wires for 4 speakers. I have done some troubleshooting and realized each of the two starboard and port speakers share 3 wires.

For example: Starboard: blue, green, yellow
Troubleshooting results:

Blue and green wires power front speaker.
Blue and yellow wires power front speaker.
Green and yellow wires power rear speaker.

Anyone know how to wire this up to get sound out of both? I'd rather not rip up carpet and floorboards to visually look at the wiring.

Thanks
 

CHARGER2

Petty Officer 3rd Class
Joined
Jun 14, 2012
Messages
80
Re: Boat speaker wiring puzzle

For everybodys future reference, found this in the archives by NYBo. Kind of figured this was the case. I guess I'll either have to deal with only 2 speakers or wire a grounds back to the head unit.

"In a common ground scheme, each pair of speakers is powered by 3 wires (R+, L+, and common -); most modern head units require that each speaker have 2 separate leads."
 
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