That Solder tab is supposed to be an anchor point for the single red wire and the black wire that are floating off to the side. This is to prevent the turning of the motor truck from fatiguing the field wire and breaking it off. Once you get it running, make that mechanical connection.
The white wire is supposed to be connected to the collector/rollers for power to the bulb and reverse unit, on the brush with the black/white wire(from the rollers).
The other black wire floating around there connected to the green field wire is supposed to be connected to the other solder tab between the brushes as an anchor point to prevent the turning of the motor truck from fatiguing that green field wire and breaking it off. Once you get it running, make that mechanical connection too.
