ldfog

This is a fantastic forum for ideas and information. Thanks to all who post here. My problem is my backup lights don't come on. I have checked the lamps with a continuity/voltage tester, and they are fine. The sockets are clean. The fuse is good. Is there a module or switch somewhere that is not working, and if so, where might it be located? I can't find it in any of the tech manuals I have.