Might be specific to Sierra.
If that breaker is to feed (or be fed from) an on board generator (and you do not have that option) there won't be a wire connected to it. I would remove the cover and look.
If there is a wire, a trace would be in order to see where it goes. Is there a "home" for a generator in the Sierra? There might be a switch over relay setup in there that uses that breaker.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW