Well ... I'm not sure about the Brava, but my 1998 Bravo had a CD changer cable fitted to the boat. BUT THIS DID NOT PLUG STRAIGHT INTO A T-69 !
I had to replace this lead (with the one included with the T-69), and use an adapter box unit which plugged via a cable into the back of the original radio.
I also put my changer under the rear seat. But didn't bother cutting a flap in the carpet. I find it easy just to lift the drivers side rear seet up, and mount the CD changer there. I didn't screw it down, but used strong double sided foam tape. Under the carpet under the seat to stick it to the chassis, then on the CD unit to stick it to the now stuck down carpet. Making sure you can eject the CD holder OK once in place.
The unit works a treat. Had no problems with it. Its been in the car about 1 1/2 years now.
