Fully expect the culprit to be the alternator regulator ,worn brushes but main cause is one of them does not make proper contact 90% of the time.
I had similar with a w124 which had random warning lights not coming on and even no glow lamp and just turning the engine over a touch on the starter would see everything ok.
If I remember correctly it was the brush nearest the actual regulator body (the first one to see daylight when regulator is removed from alternator) .
One tell tale is slightly flickering interior lights at night.