Be SURE when going in with new voltage regulator to CAREFULLY position the commutator brushes so they don't bind or
break off upon reinserting in the back of the alternator case...I had to tie down the brushes with a sring in order insert the regulator.
I changed out a VR on sunday in my 240D.
You'll find it will likely be a spring on the brush set that failed to hold tension on
the carbon brush hence not allowing good electrical continuity..I've had two VR's
fail because of faulty springs.