I recommend you buy the correct GG part for a 2012.
EE512002510 voltage regulator/rectifier
If you have all the parts and the RR has been lost, you still should have the harness with the stock connector.
I was just working on a buddy's 2012 estart bike last weekend. The RR is the same as on my 2011 bike. 2011 is the first year for estart. Use Matto's dropdown menu and select 2011 electric start, then wiring harness and you will see the RR part number (item 9 in the diagram).
http://www.gasgaspartsguy.com/OEMpartfinder.htm
Matto's 2012 listing is for a standard non-estart bike.
The 2011 fiche specifically lists the estart parts.