BD 125, noob rider with some bike problems. Please help!

[Durtyrice]

Hello friends,

I recently purchased a BD 125 motorcycle and am having a few issues. I'm able to start the bike fine, but then it loses rpm and stalls. Every once in a while I can get the bike going but when I come to a stop it often stalls. I've been tinkering with the air/fuel screw but any other suggestions are welcome.

My battery indicator keeps flashing, and for some reason 3rd gear won't show on the speedometer even though the bike itself does shift. The speedo says its still in second gear when it's realistically in third, or nothing shows at all ( no number shows up). If I shift up again it'll go to 4th and display the number 4.

These issues had me thinking it was a battery issue. I'm the second owner and realized the previous owner changed out the battery. That's when I noticed this plug (see attached pic) Any ideas on what it plugs into??

Thanks for the help!