What type of generator.. Portable or Installed. in both cases make and model.
Unable to answer with out more info.> Will post one generator
Onan RV generators (installed) are "Smart" if they are running they ARE making power. this power goes (normally) first to an Automatic Transfer switch which holds off 30-90 seconds and then CLUNK connects the generator.. Normally.
IF this is an RV install that's the first place I'd look
Portables.. More complex
NOTE: Some RV's (some older ones) have a "Manual Transfer Switch) this is a 30 or 50 amp RV outlet often near the generator you MANUALLY transfer the shore plug to this outlet to use the generator.
NOTE on Auto switches.
DO NOT HOT SWITCH
SHut off power. wait 3 minutes before either starting generator or turning on shore power... Multiple reasons for this. Life of ATS is one of 'em. hot switching with an A/C on can weld the contacts.