I cleaned all possible corrosion spots in the rear and in the fuse box.
replaced some of the fuses and cleaned the others. I figured it was good preventive action if anything.
Took the car out for a ride - the yellow appeared suddenly - and would not go off until I turned the engine off. That was Friday night.
Saturday morning I went out for a long run and gave the car an Italian tuneup at the same time. - The yellow monster Light never came on...
So today I will replace the rear brake bulbs as suggested here and if that doesn't do it I will go for resoldering the big black relay box. Thankfully I know this is really a minor issue - but failing to resolve it, does drive me nuts...