No FMS data on the F/O's navigation display. Same when trying the center symbol generator as alternate.
We did have navigation information on the Capt's display when selected to the right FMS.
From the prints there is one 429 data bus going from the right FMS computer to the center and right SGU's. I wasted hours checking intermediate plugs and terminal blocks on the back of the rack when I should of verified continuity from the FMS computer to the SGU's first..... AND THEN CHECKED FOR A SHORT TO SHIELD.
Blue wire of twisted pair shorted to the shielding. It took the whole data bus out.
Sometimes you get so narrow-minded on a troubleshooting path, that taking a step back and mentally rethinking the basics is sometimes a good idea.