My four inverters with three light tester:
Vector 2000w MSW--All three lights on
Xantrex 1000w PSW- Middle light only (open ground)
Xantrex 400w MSW- All three lights on
Sima 150w MSW- All three lights on
It gets complicated when you plug your shore power cord into the inverter's three-prong receptacle, depending how the ground prong hole is wired in there.
The inverter "chassis" ground is to the metal box the inverter guts (isolated from the box) are in, and that goes to the trailer frame "ground" but inside the inverter, the neg input is isolated from that outside box, except maybe to the receptacle's ground on some.
If you plug in the shore power cord, its ground prong can touch something that makes a path from that to the trailer frame and now because the other end of the shore cord is at the power centre/converter with its 120v ground and 12v ground there too, to the frame, now you have 12v via trailer frame from inverter receptacle ground joining with the chassis ground, which maybe should not happen since now when you open your 12v "battery disconnect switch" (if on the neg path) everything 12v still works! You still have a complete 12v neg path via shore cord/inverter because the battery is grounded to the frame too.
OTOH some inverters don't have their three prong receptacles wired like that. Some inverters don't have chassis ground lugs (being plastic :) )
It just doesn't seem to matter in real life.
