Nice buy. Enjoy your ride.
It could be a short, but probably more likely a bad battery.
Had the bike been standing for a while?
Any history on the bike?
You don't say anything about starting or if you can ride with the battery light on.
All / more info will help us to help you.
Do the dashboard lights go dim when you put on the main beams?
If so, and you replace the battery,and the symptoms persist ,then checking things like regulator might be in order.
Looking forward to a positive result.
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