If you get an incorrect value during the measurement, we are certain that there has been a short circuit because a component located on the negative side, capable of handling 10 amps, is broken. If the current had come in from the positive side, the 2-amps fuse would have protected the power board.
If the power board have been exposed for a short cut, there is a upgrade that should be done electrical system in the vehicle. This should be explained in the Adria portal under YouTube movies.
This is not a warranty case from thetford, please contact Adria for further help.
If you have any further questions or concerns, please do not hesitate to reach out to us. We are always here to help.