Elddis Sunseeker 25 motorhome

Hi, My Sunseeker is 12 years old, and Anne and I bought it 2 years ago. The 12v control panel has not worked at all for the time we have owned it. I contacted the makers and they replaced the circuit board which had burnt out, and I refitted the unit this morning. It works perfectly now, but only on the auxillary battery, if switched to the vehicle battery it doesn't work at all. Can any member, who has now, or has once owned a Sunseeker 25, tell me if it was designed to work on the auxillery battery only, or have I botched up the refitting? Any help is appreciated.