Hi Matt1616,
Transfer switch! If whacking it doesn't free a stuck contactor, take it apart and look for a loose or disconnected ˜fast-on' connector. See photo in my photo section. Normally, the two contactors are de-energized and allow either single phase 120VAC 30 Amp. (20 Amp.) or two phase 240VAC 50 Amp. power through to the PowerLine control unit. It's the PowerLine that detects 30 or 50 Amp. service.
The transfer switch energizes it's contactors when the generator is supplying power. A problem in the transfer switch which prevents the contactors from energizing prevents AC form reaching the PowerLine from the generator even though the light is lit on the PowerLine indicating generator is supplying power. Because the contactors are de-energized, shore power continues to pass to the PowerLine.
Been there, done that, on two coaches and decided to replace the transfer switch with a microprocessor controlled ESP intelligent transfer switch (also pictured) which has surge protection and also pre-qualifies the power connection before connecting the coach. I left the old switch in place, disconnected, as a fall back.
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Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back