I am retrofitting a 13 Button OBC into my 89 325I that had a 6 button OBC. RealOem shows an upper and lower harness. The upper harness is the main harness that gets replaced. The lower goes to the ambient temp sensor? The 6 button had a temperature feature, does the 13 button plug into the same sensor harness? Also I read several write ups, some had the relay box mounted above the ECU and another had it mounted above the anti-skid module. Help!