Chassis Ground points 2013 Passat B7/NMS ?

I installed a Curt trailer harness for a 2013 Passat SLE (basically just like the 2012 Passat in the trailer hitch thread) but noted no 12v showing up from the power wire to the module ground screw I installed. When I ran a wire from the fuse box ground and connected to that, then the power wire showed 12v across the circuit. I then checked the + terminal on the battery to all sorts of areas in the engine compartement but never showed a completed circuit except to the - terminal and the fuse box ground. All the other cars I have owned would show a completed circuit going to the front strut, screws on frame, etc. Car off or running made no difference. What am I missing?

Problem solved

As I was typing this, I went over everything in my mind. I went out and rechecked and found that the power wire was going to the neg terminal not the positive. The person helping me set up when I pulled the wire under the car hooked it to the RED wire which I later assumed was the positive as well. It turns out that VW uses a red wire to the neg terminal and black to the positive. Works fine now.