'98 E320 Wagon--electrical gremlins

[halfwhit]

#1. 'Defective lamp' comes up when I brake, but all brake lights work.
I did just replace a burnt out brake light bulb, off the shelf from
AutoZone. It used to be the case ('80s era) that one had to buy
such bulbs from the dealer, else the cruise control would fail, which brings
me to

#2. Cruise control does not function when headlamps are on. I did
recently replace a headlight bulb, again off the shelf. What gives?

Cheers,
Richard