Is there a electrc cover on the ceiling near the AC shroud. Get your volt meter, the black wire in the box is the hot +; the green wire is earth ground -; and the white wire is neutral. Set the volt meter to any setting higher than 120Volts AC. take the red wire and touch a bare spot with the probe on the black wire + in the box; then the black wire and touch the probe to a bare spot on the green. you should see voltage. If not do the same on the inverter AC breaker which is hot +; the ground on the meter can hooked to metal frame of the inverter. Still no Voltage then locate the trnsfer switch and keep working back to the source. ***Make sure your feet and you are not wet***