Started troubleshooting the rear fog light (tailgater scarer) on my 89 740 GL sedan. I have voltage on the grey wire and voltage to the pcb near the socket. Now here's the weird thing. I have continuity through the bulb and socket but no light! Even weirder (to me) is that when I put the socket back in to the pcb I have no voltage at the pcb. Still have voltage at the plug but none at the pcb when the bulb and socket are in place. With the socket minus the bulb in place I have voltage. Is there a special bulb that's supposed to be in there? I've tried two different bulbs in it. It's just a single contact socket.