I remember that some of the BladeZ controller boards have B+ and B- printed next to the spade connector terminals which go to the battery pack along with M+ and M- next to the terminals which go to the motor. If the controller board has these marking on it then it would be good to confirm that the motor wires are plugged into the M+ and M- terminals. The B+ goes to the positive battery pack lead and the B- goes to the negative battery pack lead.
If the battery pack is wired to the correct terminals on the main board then there should be a strong spark when making the final battery pack connection to the board, but after the big spark then the the wires should not get hot or start to melt any solder or show any signs of trouble. If after making the battery pack to control board connection anything starts to get hot or melt, or the circuit breaker trips, then the controller is damaged and will need to be replaced with an aftermarket replacement controller.
Wiring the battery pack to the board without a circuit breaker probably would not damage the board. If the battery pack was accidentally wired in reverse polarity to the board the circuit breaker would react too slowly and would not save the board and would only save the wiring harness from overheating.
The battery pack to control board wiring can be connected in any sequence however the way I like to connect the wires is to the main board first, and then to the battery pack last. I connect the circuit breaker between the two batteries first and the wires going to the control board after that. I always start with connecting the negative wire to the battery pack, and then make the positive wire to the battery pack the final connection. That is just the way I do it though and it really does not matter if the wires are connected to the battery pack with the positive wire first and negative wire last.
A good controller would not draw enough power from the battery pack to trip the circuit breaker like that. That test confirms that the main controller board is faulty and needs to be replaced.
The push-on connector that goes to the battery terminal which melted was not making good contact with the battery terminal which caused sparking inside of the terminal. I would replace that terminal with a new one and clean up the melted battery terminal with a file before reconnecting the new connector to the battery, or if you have soldering equipment then you may want to solder the wire onto the battery if you feel that the battery terminal has lost too much metal to make good contact with the new connector. Most scooter manufacturers solder the wires onto the batteries to avoid the possibility of a bad connection and melting the battery or wiring harness terminals.
Here is a photo of a battery pack that we make with the wires soldered onto it.
After we solder the wires onto the batteries then we cover the wires and terminals with heat shrink tubing and apply hot melt glue over everything to prevent short circuiting of the terminals.
Please let us know if you have any questions.