Hi there
try looking here
http://z4.invisionfree.com/lexusaltezzaclu...?showtopic=8256or break out the multimeter and go a-hunting
I'm pretty sure most/all aftermarket headunits have a combination yellow/red/orange (choose any two). one is for the battery supply and the other is for the "memory" any chance you go these two around the worng way ?. this would mean the H/U wont turn off when you turn the key off.
option 3 run a fresh ACC/key wire from the fuse box (track and trace again)