is the controller integrated into the pump or has the controller an extra-housing?
850W means it is a 230V pump. If this pump has no plug like this
This would mean you have to mess around with wires that use 230V.
This is only allowed for well trained experts with a formal examination.
Without a final expert-check of a person who has all the equipment and the formal graduiation to do so you should not repair this pump.
Additionally it is with water because it is a water-pump.
Imagine: how much money would you pay each month for the rest of your life if paying this money would bring back a person to life that you love ?
If you find a already certified 230V-switch with a 230V-socket which can be used outside and is rain-protected (IP44) and has a 5V input and your pump has a 230V-plug like in the picture above you are on the secure site.
Not that cheap but safe to use
https://www.google.de/shopping/product/13453268201721553109
best regards Stefan