My 735IA 1987 model suddenly startet acting crazy. At first, when I tried to lower the windows, the interior lights turned on. Then when I started the car again, everything worked fine. I thought... Then the central locking didn`t work. There is a clicking noise from under the backseat. Now windows, central locking, OBC, windshield wipers, and probably more doesn`t work. I suspect a bad connection to ground, but I don`t know where to begin searching.