A brake light bulb is sending power to the RH turn light.
1. It's two elements are fused. Visually inspect filaments with magnifying glass.
2. Loss of ground back there at the socket.
3. Voltage leak at socket/bulb.

Take one brake bulb out at a time to see if RH T/S light goes off. See which one makes it go off. Switch them. Do several of these test to be sure it's not both or that it's not them at all. If it's not the bulb, it is probably ground. Provide temp grounds to sockets with wire or screw driver tip, etc.

Since we haven't heard form you. you have probably found it already.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn