Td5 facelift front foglights

Front foglights (round ones on bumper)seem to have a mind of there own, , got side lights switched on then when I push top left switch sometimes fogs will not come on,No light either on switch then i can drive good few miles then will eventually come on,tried unplugging switch and remove and replace relay but still same. Also happens to front spotlights too when on full beam I know there different switches and relays, spots are on soft 'A" frame so guessing this one might be bad earth??any other ideas???

Check if fusible link FL13(30A, engine bay fusebox) and fuse F3 (interior fusebox) makes good contact, also it would be good to check the connectors behind the interior fusebox...corrosion is quite common there, and so it is at the BCU's pugs(behind the glovebox)