I just checked a 15' I'm working on. That plug goes into the black box bolted to the seat bottom. You can see it on the top of your picture. It goes on the inboard side of the plug that's already there. I don't know if it's supposed to route through that white clip or not.
And you'll need to turn the airbag light off with a scanner of some sort. Unhooking the battery is probably not gonna work for you. You can unhook airbags and sensors all day with the battery hooked up but the second you turn the key to run with something unplugged it'll throw a hard code.
Mirage videos:
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View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)