9F Overhead View of Chassis and Contact Strip

Note the contact points for each wheel, and the extra contact at the front of the loco for the positive end of the light bulb. This picture also shows the red lead from the choke coil connected to the top brush of the motor. If the motor is replaced upside down, this wire will be at the bottom, and the engine will run backwards when it should be moving forwards !

The cheese-head screw next to the red wax which coats the choke coil, provides the main connection between the left hand copper strip (negative) and the chassis. On some locos, (like this one), this is the only secure connection to the chassis.