it shouldn't require soldering, the diagrams show all plug numbers, EXCEPT the (2) red wires to the DOUBLE BREAK RELAY (if equipped).
They may have to be soldered.
It may no longer be used on replacement control board.
compare your board to the pictures of the (newer) replacement board.
If you have one and the replacement doesn't use one, you MAY be able to bypass it.
It may be a safety disconnect incase one of the other heater relays stick. The new board MAY have better heater relays...