I have a Kenwood stereo with Garmin navigation everything works but sterio sound is only upper sleeper in a volvo 780 all other speakers nothing not the 4 cab and lower sleeper. it appeared that a proper adapter was used and spliced to the radio adap
November 2nd, 2014
Use the blue wire from the kenwood nd hok it to the blue wire on the adaptor harness. This will trigger the factory mp on and your problem should be solved