I assume that you are referring to the habitation control panel. Typically MH habitation electrics use a wired return to the habitation battery negative. The base vehicle will however use an earth or chassis return system. In order that alternor charging of the habitation battery may be carried out. the habitation battery negative must be either linked directly to the negative pole of the starter battery, or connected to chassis.
As 2002 is quoted, for presumably the year of registration, and assuming that it is a Fiat base vehicle, then the main starter battery chassis connection will be under the front end of the battery, forward of the RHS engine mounting.
I am doubtful as to whether the cause of your problem is, a faulty earth connection.
