Although you could power the gimbal from the balance plug of your flight battery (assuming you have 12v gimbal) you still need to open up the P1 to connect the pitch and roll leads from the gimbal controller board to the correct ports on the NAZA flight controller.
Since the balance plug leads are short (making routing wires difficult) its much wiser to power the gimbal from a self made soldered connection (shown in the attached photo) via a connection made to the P1's main board.
After that you need to turn on the gimbal the using the DJI Assistant software and then follow instructions from your gimbal manufacturer to calibrate the gimbal's pitch and roll.
Be careful opening the P1 shells.... there's GPS wiring connected between the bottom and top shells that can be broken if you separate the shells too far apart.
Attached is good photo showing how all the connections are made...
If you have little or no soldering experience, I recommend you find friend (or a radio or tv technician) to do this work for you.
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