Patrick wrote:
I have some vinatge headphones (Sennheiser HD424) and want to attach a new
plug.

Which color wires are the positive ones?

The colors in one of the leads are red & blue and in the other lead black &
yellow. (No wire is used as screening - there's just two wires in each
lead.)

From my years of tinkering with old stereo headphones as a teenager, I'm
going to confidently guess:

Black - Left Ground/-ve
Yellow - Left +ve

Blue - Right Ground/-ve
Red - Right +ve


Martin