Power steering.

[Bluebell]

V8Coopman, you are obviously correct. My thoughtless error. I will edit my post. The actual purpose is to stop a length of wire down the column from being (possibly) repeatedly twisted when turning the steering wheel. The slip ring and brush arrangement allows the wiring to remain static in relation to the turning of the column and therefore reliable. (in other words, from the horn button to the slip ring there is no relative movement)