The dash lights were most likely wired by the chassis manufacture. You should be able to get a wire diagram from the manufacture to see what feeds that fuse.
A guess before that would be the headlight switch or the block off the ignition switch. It is unlikely the dash light would be feed directly from the power distribution block because that would lead to frequent dead batteries.
Have you checked the dashboard dimmer wheel on the headlight switch to make sure it has not been turned to off.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles