My Titan did not come with a hitch. There are many on the market. The dealer OE (999T5-WQ200) looks like the best fit snug up under the bumper but it is about $70 more than some of the aftermarkets (like Curt). I am not convinced I am a fan of the round tube hitches.
Any advantage to getting the OE hitch?
How hard is it to wire to the 7 pin connector?....is it prewired to the rear of the truck?
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The factory/dealer hitch comes not only with the 7-pin adapter, but the 3 relays you will need to make the electrics actually work. These can be pricey if sourced locally. It will also come with all the hardware you will need.
Price the 7-pin adapter, the bolts, and the relays, separately, and the price point comes much closer.
Yes, Titans come pre-wired to the back - through the relays you probably need. It is a good quality hitch and I have no regrets buying mine through a dealer. I got mine through Courtesy in TX when they were having a %-off promotion, and even though the freight was expensive (it's heavy...) it fit perfectly, had everything needed in the box, and came with instructions.