Mine refer quit a few months ago, everything about it quit, would not cool at all. Anyway it turned out the little black device in the back of the unit, attached to the cooling coils had failed. This is attach by wire to the interior light. Called Norcold and they sent me a "free" of charge replacement thermister assembly and everything began to work again. It was an easy fix for me and I think anyone could install the thermister and wire, its an easy unplug and plug in wire. Look here for the parts list:
http://www.thetford.com/HOME/PRODUCT...8/Default.aspx Then give Thetford/Norcold a call.