My 1999 C5 has HUD and the MPH is no longer showing. Is this a bulb replacement or an electronic failure in the HUD? What disassembly is required? All the adjustments for the display appear to be working, brightness adjustments and the mirror adjustments are functioning as normal. If upper dash panel needs removal, can you point out fastener locations so I can get at the unit.
Thanks,
Neil

 

Welcome to the forum.
The only recommendation I can give you would be to get a copy of the factory service manual and go from there.