Hi Quinc if it does not work out with noahmercier , these controllers
are 36V 1000W 32A that may fit the bill. These are About 22 bucks and 2 - 3 weeks shipping. (48V 1000W yk33f are similar in price)
You will need to make jumper wires to go from the stock Razor brake connectors to these or change the connector on the controller (both are female).
If you find a controller that only has 1 brake connector, just use splice or jumpers from both brakes to the 1 connector (that is what Currie does
via Ebay in Florida has pretty much the same thing for 2x the price but you would get much quicker and should be pretty much plug & go..
I also have our stock MX650 controller (from 2011) that I don't think I'll be using anymore that I could part with for the right offer
. I did run it for a little on 48V and it seemed to be fine. I'll even include the 6 wire twist grip. Guess I would ask $30 shipped.