Audio Systems: upgrading stereo system in a Boat, roadmaster speakers, ground cables

Question
I recently bought a 1992 Bryant boat that had a Seaworthy brand AM/FM/Cass and two Roadmaster 5.25" speakers.

Today I tried to upgrade the head unit from the old type Seaworthy to a much more modern Kenwood AM/FM/CD/HD Rado/Sirius compatible head unit and I am having no luck.  The original system in the boat used a common ground system for the speakers but I think someone has hacked that up to install the cheap Roadmaster speakers.  I connected the power cables and ground cables the the Kenwood head unit and have power.  The head unit seems to be working correctly - I can scan AM and FM stations and play CD's but I have NO sound from the speakers.  I even tried wiring a speaker directly to the wiring harness from the radio with 2' of speaker wire and NO sound is coming out.

I am guessing that since this is a boat I am having a ground problem for the speakers....?  Can you take a 5.25" speaker and run a '+' and '-' wire directly to the + and - wires in the head unit harness and achieve sound?

Any help, advice, diagrams, ANYTHING is appreciated.

Thanks

Answer
each speaker needs to have possitive and negative  the amplifier inside the radio are individual
if you connect the grounds together the radio can get damage , it will be best to run  all new speakers wires it is not that dificult use the old wires to pull the new wires

good  luck