Current pickup strips can be found in the spare parts bag. They are provided for rubbing on the inner side of the wheels. But as they fall into the crook of the flank, they must be bent at least 1 mm, otherwise they do not make contact.
As wires will have to be soldered, I recommend to pre-tin the strips, to the inside, i. e. side opposite the bending. Do not put too thick a layer of tin, otherwise you will not be able to install the strips into their housing.
The strips are slided under the bogie, after removing the brake equipment, into a slot provided for this purpose. The small tongue protrudes about 2 mm above the bogie frame.
Reassembling the brake equipment will then be sufficient for the strips to be held in position.
Prepare two flexible wires as thin as possible, 80 mm long. Personally, I use 0.5 mm wire sold by ESU. I try as much as possible to respect the NMRA colour conventions, so here: red wire for the right rail and black wire for the left (with direction of movement end #1 forward). Needless to say that the wires of bogie #2 must be reversed! These wires are stripped — very little: 2 mm are enough — and tinned.
The soldering must be done quickly, the wires being horizontal so as not to rub under the frame, and going towards the front — see photo below. Be careful not to damage the bosses that are used for 2-point suspension, and which are very close to the tongues.
There is no intervention to be made on the chassis: the bogies may then be reassembled by passing the wires through the T-shaped opening near the hooking of the drawbar spring.
The picture shows the bogie #2 already assembled, and #1 waiting.
Note the groove in the chassis going from the T-shaped opening to the other end, passing under the ballast. Its utility is not clear to me, for it can contain only one wire, and therefore cannot be used to connect the two polarities of the bogies.
Ø 0.5 mm electrical wire
3.59 € per 10 m — price 2015
ref. ESU 519xx at ModellbahnShop-Lippe