Hello all. Need some help/input from the experts. I have a 2010 F-450. The radio is the factory unit with the single CD player & satellite radio. It is the traditional-style green light display, not the LCD Nav unit. My problem is with the dimming of the electronic digital display (where the radio frequency or clock readout is). At night when the headlights are on this display will sometimes dim with the rheostat like the rest of the dash panel and gauge illumination, but sometimes will stay full bright. And it is very annoying at full bright at night. The weird thing is the rest of the radio buttons and lights will dim properly and consistently- it's just the digital display that will go full bright. It does not flicker, or change in relation to a bump in the road or something similar that would scream out "loose wire." It just sometimes dims, or sometimes is full bright. Occasionally it will change while driving down the road, but due to anything noticeable.

I've taken it to my dealer (it's still under warranty) three times for this now. The first time was for this problem and a cracked plexiglass instrument panel cover. They completely ignored the dimming issue and just replaced the plexiglass cover. (However, they only had the cover held in place with the dash - no screws in any of the holes, A socket wrench and the screws that were supposed to be holding the cover in place were on the floor of the truck when they released it to me.) I took it back, they took a week to install the screws and a new head unit, called me and said "all fixed." I picked it up only to immediately discover that the dimming issue with the radio had not changed at all. (It was quite clear at this point that they don't bother to actually check their work once they think they've fixed something.)
I took it back a third time. They kept it for another week, and then called me and actually said the radio display was not supposed to dim on that head unit. According to their interpretation of the wiring diagram only the very basic unit dims, and since my unit had satellite, it was not the basic unit. The fact that it actually did dim about half the time (and that they spent a week supposedly working on it before) didn't dissuade them from trying to convince me that it's supposed to be full bright all the time. At this point I told them I was done with them and to put it back together (which, since it was warranty work, was probably what they were hoping I would do from the get-go.)
So now, my question to all of you is what the heck is up with, a) my radio, and b) my dealership's interpretation of the wiring diagram.
Thanks for any and all input and advice.
Ted

 

Still hoping for some insight - anyone have any knowledge on this?

 

Did they swap out the radio as a problem isolation first step? I guess not, from the way you describe their work.

The dimming signal to the radio is on one line (wire) and affects the button backlight as well as the high voltage driver for the vacuum fluorescent display. They are not independent. If the radio buttons are dimming then that means the radio is receiving the illumination signal, and perhaps the VFD driver is not able to interpret the signal.

Based on what you describe (and only that, without actually seeing it), I believe this is an issue with the electronics within the radio head unit, not the wiring to deliver the signal to the radio or anything else backlit on the dash for that matter.

If you're not getting any help from the dealer, you can test it yourself with a meter. Identifying the illumination signal wire should be easy as it obviously changes in proportion to the backlighting level. This will confirm that the dimming signal is being sent to the radio, and it is the fault in the radio where it is not reacting to that incoming signal. You can also determine that that point whether it is simply an analog range of voltages proportional to illumination level, or if it works based on pulse width (on/off cycles, changing the duration of the on cycle vs. off). Once you have that figured out you can run the radio on a test bench OFF of the vehicle and manually input a signal similar to what you have determined through the tests done ON the vehicle - and if the dimming issue is still present - where the button backlighting responds but not the VFD screen, then you can say with confidence that the issue lies with the radio, and should be replaced as a whole module under warranty (well, 2010, I'm assuming it is still under warranty).