On my 2000 Horizon, the rear speakers were attached to the back of a combing panel, and the front hidden behind cloth. Had to use a mirror and socket wrench to loosen hex nuts from the back. The combing panel had the screws glued into it, so the nuts remove from the back. Had to work with a mirror and flashlight.
The combing panel also removes the same way... find nuts and/or screws by reaching up to the back side with mirror and flashlight.
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings