Is the headlight switch supposed to light up?
 

On a 124? I see an orange plastic dome on the switch, and I'm wondering if there's a light bulb back there somewhere that is burned out.

TIA! :D

It only lights up when you pull the switch out "two clicks" to enable the rear fog light.

If it doesn't illuminate, you can pull the switch completely off to reveal the tiny bulb that resides in the shaft. You need Keebler elves to get it out!:D

The orange bulb inside the switch won't light on a '91 300E because I don't think the standard 300E had the rear foglight option. The 300E/TE 4matics have the rear foglight option, therefore the light will come on. The switch positions are backlit by a small light that is accessible by removing the knob, unscrewing the switch holding nut, and prying the plastic trim piece out. The chassis manual has a piece on this including a pic to show you how.

someguyfromMaryland

I had a 89 300E and it had the rear foglight, its safe to say the 91 does as well.

Thanks G-Benz and SGFM...
 

My 300E does have the extra fog lamp bulb on the rear driver's side, so I guess there is a burnt out bulb behind there.

I will disassemble and replace hopefully without the need of elves. ;)

If your headlight switch illumination is working, just pull out the knob without disassembling anything.

Otherwise, follow "someguyfromMaryland" advice...