Group of two cars, service call for one car not running. Upon arrival, cars lights are not working. Cop B is working, Cop A is not working. Car will run from COP B with no issues other than car lights. Notice that K2 relay is on on CCBN board keeping the lights on battery back up. Replace CCBN board, still same thing. Found corroded buttons on COP A, replace them, still same thing, replace mull board in COP A still same thing. There are no fault codes in the system at all. We unplugged everything from mul board on COP A except for the CCBN and COP B connections still same thing with the K2 relay. We have done the LON download. Looking for suggestions.