I have an '06 Xterra S 4x4 that did not have the factory tow prep package. A local aftermarket roof rack and hitch dealer set me up with Draw Tite's 4-pin harness expecting it to work. When I plugged it in, I had the same problem as you guys - I could light everything on the trailer except the parking lights.

When I took this problem back to the aftermarket dealer, they were surprised to find it didn't work. Apparently, this was the first they had seen of the Xterra issue. Upon calling Draw-Tite's parent company for tech support, it turns out that Draw Tite does not support the new generation Xterra's that aren't pre-wired for towing. All they sell is the cheap Mickey Mouse extension cord.

If you bought a 4-pin and run into this problem, here's what you need to do:

- Go to your Nissan Dealer
- Buy a 7-pin tow harness kit for $55
- Skip to the part in the instructions where you install the relay harness and relays under the passenger-side kick panel. These relays will activate your running lights.
- Save all the other parts for scrap. Your 4-pin should be fully functional now.

I thought I would be able to buy the relays and the relay harness individually for cheaper than the 7-pin kit, but it turns out the kit is your most economical option.