Might want to call Freightliner, I have em on speed dial. They are really nice.
On mine, there's a primitive computer in the dash, called the "LBCU" or "FUBAR" or something, and the gauges are connected in serial out of that thing. If the first one in line goes wonky, none of them work.
If you have that, Freightliner will send you a rig to hook em up in parallel. What they won't tell you is, sometimes if you hook em up in a different order (hopefully, with the bad gauge last in line) sometimes it'll start working again
2008 Tiffin Allegro Bus