Hello Bart, i'm no expert, but as far as i know the 230 and some 250's are mounted on the wing (fender, depending where you live in the world) see below from another post, if you search the forum there are plenty of posts, and some pictures
A 250SL should have an external fender mounted voltage regulator.
You will find it on the right (near the inlet manifold plenum) inner fender near the shock tower.
