Today’s Lego City train sets include a PowerFunctions motor that works very well for short trains. However, if you add additional wagons, the traction of a single motor is not sufficient. An obvious way to fix this issue is adding a second motor. Another option is adding weight to the engine as the motor has power for some additional wagons but there is not enough friction between wheels and rails. In this posting I discuss an issue with the first approach: While adding a second motor sounds like a straightforward task, you will encounter a problem: The motor of the second bogie must be rotated so that the cables of both motors point towards the holes at the center of the engines base plate. Due to the rotation, the motors move in different directions. To make the second motor go in the same direction, the polarity of the motor must be changed. This can either be achieved by swapping the cable leads either in the plug, in the middle of the cable or inside the motor housing. I prefer the last approach – swapping the leads directly at the motor – because its easier to open the motor housing than the plug and the modification will not be visible. What you need: PowerFunctions train motor Soldering iron Torx T6 screwdriver Tweezers (optional, helps with getting the gears in place again) Instructions: Remove all six screws at the bottom of the motor and open the motor housing. Remove the gears and axles. You can just take them out, they are not fixed once the housing is open. Remove the motor and the clamp piece that is used as strain relief. Unsolder the leads from motor. Put the motor back into the housing at its original position. Cross the wires and arrange the wires and the yellow inductor. It is possible to cross the leads below the clamp piece, it still snaps in with the crossed leads below it. Solder the leads to the motor. Restore the gears and axles. This works best with tweezers. Close and screw down the housing. Motor after opening the housing:   Motor removed from the housing, leads crossed:   Unsoldered motor:   Motor back in the housing:   A folIow-up on how to change the polarity of Powered Up motors can be found here.