Amby, Mazda 5 rear interior panel removal to gain access to tail light plug, video link below shows right side removal, procedure on left side would be the same. You can stop video at about 8:45. as you will not have to remove anything else to get to tail light plug.
If there is nothing wrong with existing harness, wires and bulb sockets are not damaged it can be reused with the new tail light just by unclipping it from existing tail light and re attach to new taillight and save a lot of time and work.
Good luck.
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https://www.youtube.com/watch?v=9evxNTmF...