Need help with Electrical problem

I have a 2006 Four Winds 29' Class C Motorhome. Recently, the 12V coach power stopped working. I just replaced both batteries and charged them and changed out the battery cables, the engine starts fine. It works when on shore power and with generator but when I try turning the cabin overhead lights on using battery power, nothing. Also, the generator won't start unless I jump the starter solenoid directly to the battery. When I jump to the switched side and hit the "start" button, the gen starts fine and runs. Without the jump to battery, when I hit the start button, it just clicks. I cleaned all the terminals and think it has something to do with the 12v problem. I asked a dealer and they said I need a new power distribution panel, the transfer switch is bad. I have also been told it could be the transfer switch which is not located in the power distribution panel. I don't want to spend $200 plus to find out it wasn't the panel at all. Any experts with advise??

Mike