http://iberplace.com/146...ros-db-class-1-ac-ca.jpg
http://fs5.directupload....ages/160112/wfnb2qhu.jpg

The bogies of these 264mm Roco coaches are designed to accept an AC slider or wheel contacts. You can see the two little pins sticking out of the underside.
Most Roco coaches of that era were delivered with a small black piece with two holes and ends that are slightly narrower than the middle.
If you take a Roco slider, you have to undo the metal clips that hold the slider to the plastic piece that has the screw hole and replace it with the piece that was supplied with the coach.
You then run the cable through one of the holes underneath and press the slider so that it is affixed by the two pins into the holes.

My experience is that the longer slider is easier to mount. The short slider has a shorter spacing between the clips, which on some models did not fit the supplied plastic piece.

The other alternative is to shave off the little clips and to simply take a regular AC slider and glue it or otherwise attach it to the underside of the bogie.

Regards

Mike C