Bought my 1991 Maxima Few days ago, only front passenger speaker works. (Bose) It cuts in and out a little and volume will not go up to loud. Factory head unit seems to work. I'm getting power to all speakers according to my poke light.
Also, the turn signals do not work in the back. Checked bulbs, they are good. Fronts when turned on just stay constantly lit. The signal indicator on the gauge cluster does not flash either. Was told it could be a ground. Is there any common ground wires that could go out and cause something like this. And the fuel gauge is a little weird. Says I'm full or 1/4. New to the site sorry if it's in the wrong spot or if there is already a thread for this. Tried plugging in a new speaker to the rear and I could hear sound just extremely quiet.

 

Blose amps have failed. Bypass the amps

 

Like James said try bypassing the amp in the trunk and as for your turn signals in the back are your flashers/hazard lights working? If not check the conection on the back of your hazard switch on the dash. If it's unplugged or slightly unplugged not making a conection your turn signals will not work either. The other thing to check is your fuses.

 

Check the sockets and bulbs for corrosion...