I had the same problem with my 2007 Explorer Sport Trac. The wiring harness / connector that companies are offering that should work with the Fords put the dimmer wire in the connector where Ford USED to put the dimmer signal. Apparently, Ford moved the dimmer wire one hole up on the Ford connector. Also, they don't send 12V to the radio anymore. The dimmer signal, for full bright, was around 3.6V.
I ended up running a wire from the light that illuminates the P R N D 3 2 1 display on the console up to the wire going into the AVIC for dimmer. The console illumination had 12V and dims w