On the left side of the bike, next to the battery box there are two pairs of connectors that are exactly the same shape.
One is for the spark signal and the other is to charge the battery. If you mix them up, you will get no spark.
Look for two pairs of connectors, one with have a pair of wires, one brown and the other black with a white trace line the other connector will have a blue and a green wire.
Make sure that the colours match on both sides of those connectors.