The positive pickups are on the right (bottom of this photo). A tag protrudes through the weight onto which is soldered the other end of the black lead from the loco. The other tag springs up slightly to make contact with the weight. The negative connectivity is through the weight, through the mounting screw and via the coupling as seen in the next photo. Note that the pickups contact the wheels on top of the flange, and that it is not possible to remove the copper contact strip without destroying the retaining melted plastic. If the copper has lost its springiness, then pop the wheels out, bend the strip down slightly and replace the wheels. This can be done without taking the tender apart.