Hi there l just purchased a 1997 Mercedes Benz S420 yesterday and l am facing a problem. l tried to turn on the fog lamp and it worked the first time but then later on when l tried to turn it on it would not function. Can someone help me out on what may have happened thanks!
No both the bulbs were working before then after l turned the switch off, when l tried turning it back on only my day lights, highbeam,low beam worked not the fog lights.

Check for a bad bulb..is one working or none at all? May be a bad fuse or relay if none.

first check the bulbs, replace if filament if broken, if not then check the line if the socket are plug in properly, you may also want to check if the fuse is in order (located on the left side of the engine compartment beside the brake booster/brake fluid reservoir. If everything is fine in these areas then check if the switch is working properly, and if not you may need to replace (quite expensive for this part).

l think it may be a switch problem.

l assume you know how to turn on the front and rear fog lamps? If not,

Turn the switch to your right then PULL the rotary switch towards you. The first click is the front fog, while the second click is for the rear fog. It is shown with a light icon on the left of the switch. This will show that your switch is working.

Check this out first if this solves your problem.