When I was wiring my aux lights...
Option #1
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Under the left side cover there's a connector for the OEM aux power outlet.
Since I moved my ignition into the left side panel, I clipped the connector and used that power feed.
Option #2
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If you want to go under the right side cover, the lead for the brake light are on top of the bundle in front of the ECU. I believe the 'live feed' for the brake asembly is a three wire set with a blue wire, yellow wire, and black wire(?).
You can confirm by keying your ignition and putting a 12V test light into the back side of the connector.
Option #3
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You're other option is to run a hot circuit and hide a switch.
I have a hot circuit and I put the switch in the top of the left side cover up under the lip of the seat. You can't see it unless your looking for it and I can still use the switch when I riding down the road by reaching under the lip of the seat.