The upgrade kit has a diagram of the wiring, the track power comes in on the 7 pin connector. Pins 1,2,3 are the tach reader, 4,5 are the chassis (wheels), and 6,7 are the center roller.
In your picture, one of the leads to the tach board appears to be missing, that's going to be a problem.
Do you realize if you have a 3V board with the standard connectors, you can remove the connector bodies from the old 5V board and replace them on the new board to avoid all the connector swapping? Also, you are going to have to replace the battery holder, charging jack, and the speaker.
