little orange triangular light...
 

I am probably revealing real stupidity with this question - but what exactly is that little orange triangular light that is immediately to the left of the fuel gauge on my 1983 300D? I can not find it in the owners manual. Sometimes it's on (when the tank is full and when it's nearer to empty) and sometimes it isnt on. There does not appear to be any sense to when it lights & when it's not lit, like fuel level or cold engine, etc. Maybe it is malfunctioning.

That is your reserve indicator. If it's working correctly, it should light up when you have only a gallon or two of fuel left. If it's coming on at other times, something is wrong.

BTW. The only dumb question is the one that isn't asked.

Have a great day,