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