Ok. I found the heat shrinks and I placed them in the wires and connected them to the motor. It seems they are in the right position, since I followed the Singer 15-91 motor manual. By the way, I also found the picture of the "knot" thepolyparrot was talking about in the same manual:
http://parts.singerco.com/IPinstManuals/15-91.pdf
Now I have another wiring question. I need to replace the wire in the motor and I bought it at sew-classic. However, they are not color-coded, but there is one side of the wire with lines on it and the other one plain. Do you guys know which side of the wire goes in the red terminal and which one goes in the black? Is it too complicated to change these?
(I know the responsibility on changing the wires is mine, so if you know electricity, please don't be afraid of giving your opinion)
Thanks!