Modern Vespa

I am looking for help on how to properly wire my aftermarket heated pad that I installed on my seat.
Specifically I need to wire it so it turns off as soon as I switch key to off or lock position.
At this moment it has a switch but is wired directly to battery, I am going to move the switch to buttons (found button already) under handlebars but thow to wire it is my lack of knowledge.
Will appreciate all the tips.

I attached related diagram I found, but that tells me nothing.

If you have a 2016 Mp3 Sport there should be a 5 pin wiring harness under the handle-bar plastic. These are the 5 pins referenced in the diagram as "heated handles and legs cover device preset" outlet.

This is intended to plug into the wiring hardness and relay system that powers the Piaggio branded heated grips and leg-warmer. Be warned that it does move with the handle-bars so don't tighten things up to much and be aware of where wires might have friction wear.

https://www.piaggio.com/us_EN/accessories/vehicle-accessories/tech-scooter/heating-accessories-control-unit-2s000122/

It turns on and off with the ignition switch. You could tap into this plug but you would have to use a volt-meter to figure out the polarity of the plugs, voltage, etc. You could also buy the official unit ($294 + tax and shipping) then use the outlet intended for leg-warmers to instead power the seat heater.

But be warned, Piaggio's are very temperamental when it comes to the wiring harness and electrical system. Its very easy to burn out the wiring harness, blow a fuse, or worse trying to tap into the factory electrical system. I have messed with it to install LED tail-lights, LED headlights, etc and so far have not caused serious issues. Proceed carefully with lots of testing and you should be okay.