Rear cargo power adapter?

I know many Renegades came with the power outlet in the rear cargo area, but mine didn't. However, there is a round cap, and behind that is the pigtail for connecting an outlet. But I'm having trouble finding an aftermarket adapter that will fit. I've tried a few from Autozone/Advance but they are either too large or too small, and I don't wont to start hacking apart plastic before I've even made my first payment.

Does anyone happen to know the dealer/mopar part number for the factory outlet?