Okay I have a solution to your problem. I have had the same thing on my Ford F-250 6.0 diesel with the Gauges not working, everything lights up etc... I just fixed it today actually based on the responses to this forum. I think that the main problem was the ground wire after all. My banks power would only work during heavy rains so that gave me a clue that there was a bad connection.
Try first checking the ground cables, there area two of them, and they may not be directly related to the wiring diagram, it may be a ground wire of another system that you plug into.
On my truck i noticed there was a ground just above where the six gun board that goes near the steering fluid reservoir (on the top right side of the truck wall just under the hood). I basically just took the bolt out, sanded down the ground cable where it attached and screwed it back in. this may have done the trick. the other ground is readily apparent and probably is not the problem which is connected to the firewall near drivers side (you can easily trace it from the banks board wires)
Again I just basically took all the connections apart and followed where all the wires go and found two fuses on the wire paths, one i believe was like a 5 amp fuse the other a 2 amp, I made sure they both worked as well, and the two amp had some white residue so i cleaned it up and put it back in. To access this 2 amp fuse i had to take my right battery out (While facing the truck) and found it underneath the 3 wire plugs that go into the side wall just right of the battery.
Anyways try that out for beginners, it is very easy maybe took me an hour or two but thats only cause i was taking everything apart if i had to do it again it would only take me like 20 minutes.
Again whats under your hood may be oriented differently but it should give you some hope!
--- Update to the previous post...
Ok see it right there above the steering fluid cap? Make sure that little nipple is inserted into that hole where the bolt screws in, it was not on mine and I believe that is what fixed the problem.
http://forum.mopar1973man.com/webkit-fake-url://12725250-DF7A-4B81-88E2-DAF83A3DA7B5/image.tiff