First ignore all reference to L-2 that is for a 50 amp setup. Follow instructions in the manual or on the cover.
ManualL-1 is the black wire in the shore cord.
Line neutral is the white wire.
Green wire in the cord goes to the lug in lower left corner. It should be green.
Generator wiring should be the same as the shore power cord. Wiring to the rig should be the same.
There should be no jumpering and splicing with wire nuts. Maybe former owner had problems and splice around transfer switch.
Should ask what size genset you have? Some rigs had 30 amp shore power and genset larger to handle two AC units. If the genset is like a 5000 watt, then L-2 from genset would be connected.