It just so happens I bought a brand new Headlight Assembly for my own 2016 Mp3 500ie Sport. Description of headlight plugs below.
What are the circumstances behind the request for a part number?
Are you also installing a new headlight assembly or did a part go missing or break during a maintenance cycle?
Which part are you looking for in the picture? The plug the bulb goes into? a retaining fastener? the wiring itself? Its not quite clear which part is the topic of the request.
Pulling the new assembly out of its shipping box I see that the left-side has the full plastic assembly for a low-beam headlight. The right-side however is just a plug for a standard headlight bulb. The attached photo is the headlight assembly oriented as it would be facing forwards on the bike if it was mounted.
The headlight assembly comes as a complete unit with all the wiring already installed including for the bulbs. So if its missing a sub-component such as the little plastic retainer or clip for the bulbs you might have to improvise something or buy a whole new headlight casing.
The assembly is number 1 on the list and is pretty expensive.
https://www.parts-piaggio.com/piaggio-scooters/500-PIAGGIO-SCOOTER/MP3/2016/MP3-500-Sport-ABS-E3-E4/Electrical-system/Front-headlamps--Turn-signal-lamps/1218/23/20642/2718