ford f150 vs ford 500 illumination?

Ok,  Here's the deal,  I have a 2006 F150 that I got the OEM sub for and found out the head unit was not sub capable.  I search for almost a month trying to find the F150 Sub capable head unit,  but the closest thing I could find was one from a 2005 Ford 500/'montego.  It works great,  but the illumination is not right.  This radio lights up when the ignition is turned on not with the headlights are on,  and it will not dim.  So,  I thinking maybe I can move the illumination wire to fix it.  I know the blue/red wire on my F150 is the illumination wire,  but I don't know which pin it should go to on the F500/Montego.

Anyone got any ideas?

Thanks

hi,

The illumination (backlighting) is controlled by the MS CAN bus on the 500/Montego.  There is no direct connection into the radio for that function. 

m

Are you sure on an 05 Ford 500?  I thought 2005 was early for the can bus.

from my contact at the dealer, 05 does have.  showed me wiring diagrams of vehicle.

m

Well, that sux.

So exactly how does the CAN/BUS tell the radio to to illuminate?  There's got to be a way I can bypass it.  Everything else on the radio works fine,  but with it lit up all the time,  they display is dimmed and it is hard to see in the daylight.