Tusk Aftermarket light and turnsignal switch

[pipexs]

Hello guys I'm trying to connect this tusk turn signal switch to replace my old none working oem switch. I figure since I had it in my garage to try and replace it with this one. Now on the instructions it says to plug the turn signal main however I can't identify wich is my turn signal main on my 1981 XS 400. Does anyone knows wich wire would be the main turn signal wire?.

Thanks