Sudden 12 volt failure

hitchglitch

We are in France at our final destination with mains hook-up and the 12 volt system is fine at the moment, however, every night halt when I disconnected the EHU next morning the dc panel went totally dead. Once, when I plugged in the car, it came on again so when we stopped for breaks the internal caravan battery system worked fine. Next day, unplugged the EHU and panel dead again.

Checked the battery and it is fine so it sounds like an intermittent fault in the dc system. Bailey Valencia Series 1.

Any ideas? Does the control panel master switch operate a relay for the dc auxiliaries? If so, maybe the relay is tripping with voltage spikes?