There will be three wires - one the Neutral return - One the permanent AC supply for the light - and the third the variable AC for the drive motor.
For a picture of the wiring use Google & Select Images
Enter the text Sewing Machine Wiring.
You will see many drawings of the layout - not particularly complex.
From what I can gather # 1 is the Neutral return and # 3 permanent live for the lamp.
Just wire these two - and the lamp should work on and off.
Then you can be sure that #2 is the motor control wire.
Good luck...
April 2015