Great first post. Welcome to the forum!
This may be a bit late, I'm new to the forum. Check the ground straps (wires) between the body and the engine and the ones under the dash for the gauges (there should be a bare metal bracket with several wires that acts as the ground bus. Had a similar problem with my '94 F250 years ago, stumped the dealer. I'm an Electrical Engineer, found it and fixed it myself...