I've always believed that to be the case, and I'm sure I've had cars in the past which would switch off the fogs when you switched on main beam (makes sense really, if used properly - in fog).Foglamps should be wired to come on when you use your dipped headlights - Spotlamps should be wired to come on with the mainbeam
However, I have just wired up my fogs and followed Geoff's BWM wiring manuals to follow the OEM layout as closely as possible - and the fogs are actually wired to operate with the sidelights (and a separate switch of course). So, if you are in fog and switch on your main beams, the fogs stay on. No use in fog, but handy when you are using them as "ditch & pothole finders"







