Additional info after messing with this thing for a week....he system recognizes that SOMETHING is plugged into the CD changer input-prior to the install, the "mode" button only toggled between the radio and the in-dash CD player, and now when I toggle through, it tries to show the CD changer, then flips over to the Mediabridge display (iPod song titles or my BT connection), so at least that part of it is working right.

I still get NO audio in any Mediabridge mode. Even turning the iPod up all the way, turning the MB setting to 4 or 5, and turning the CD 53 up as far as I can does nothing-I don't even get any electrical noise.....just dead quiet.

I've got signal at the plug that plugs into the back of my CD53. When I test at pins 8 or 9 and pin 2 on the plug that goes into the back of the CD53, there is signal, and, according to the schematic for the CD53, those are the right pins to have signal going to for the CD changer input to the CD53. I'm using an earbud cut off of an old pair of headphones, with stripped ends soldered down to prevent unraveling, and I get music through the earbud on both channels.

Does the input signal need to be a certain voltage for the CD53 to pass it through to the amplifier? That's about the only answer I can come up with at this point...maybe the signal is too weak, and the CD53 just isn't seeing enough of a signal to trigger the passthrough. What would the normal output voltage be on a CD changer?

Or maybe I'm freaking crazy...grasping at straws trying to make this thing work for a week will do that to you.