For those of you that own an 06 Sonata GLS and plan to install a
aftermarket stereo, be advised that scosche is sending wire harnesse
that have an inline circuit board. the circuit board is covered by
little black plastic cover. The circuit board contains som
capacitors and some resistors that will severely degrade the audi
quality. You will need to cut all the wires attached to the circui
board and simply go wire for wire, attaching the wires to th
corresponding color. This will allow the amp in your head unit t
power the speakers. There is a harness that scoshe makes that doe
not have the in line circuit board but I am not certain of the mode
number. I cannot claim to have figured this out myself. Anothe
reader of this sight, John, figured this out as we were both havin
the same problem with poor audio quality. I thought this would b
helpful to anyone else attempting an install in the near future.
My dash looks great with the aftermarket head unit installed.
encourage anyone else to do the same

Keit