I have two scooters and both had the wires under the deck, at the front very close to were the other wires that goes up the stem. I removed the front plastic cover right behind the wheel and found the wire in the front right side (on the newer dual motor scooter).
I bought both without a limiter on the speed so the wires was already cut, but from what I could see they were cut at their original location.
I expected the dual motor scooter to have one for each motor but it was one wire (one cut into two when the speed is limited), like the single motor one which is likely a be rebrand of the Joyor Y9.
I used waterproof button switch and connected the two wires. When turning on/off the speed limiter I turn the scooter off, then press the button and turn back on.
On the bigger switch the wires are connected to the “same color connections” (the copper looking one not used) using longer wire and zip-tying the button switch behind the controller. I used a soldering iron for soldering extended wireing and the connections to the switch.
I used a soldering iron and connected the wires on the smaller switch to the two wires on the scooter. I started out by just using a small plastic wire connector which worked fine too, just more obvious and harder to hide.
(Sorry about the poor English, hopefully it’s understandable)