On my ONAN, if I go to the outside switch (So I can hear it) And press the STOP and hold it, after about 30 sconds the light comes on and there is a clicking sound click,click,click (the fuel pump has cut on)... Wait another 30 seconds and press START. and you hear one much louder click (The solenoid) and it starts.
If you hear the clicking sound which one associates with low battery in a car. Then there are two possible issues.
1: Same as the car (Bad battery)
2: Bad connection or wire.