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 and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW