1: Download and install
Content manager.
2: Open Content manager, click on the "content" tab and select your car.
3: Click on "CM Showroom" at the bottom.
4: In the showroom, click on the material on the car you want the wireframe for. I'm guessing it's the main car body.
5: In the menu, click on the 3 dots next to "TX diffuse"
6: Click on "view mapping". (Or click on the small arrow next to it to select a resolution)
7. When the wireframe appears, click on the disc to save it.
8: The wireframe is saved (on Windows 7) under C:\User\<yourusername>\AppDataLocal\ACTool ContentManager\Temporary
Afaik, this is the only way to get the wireframe without extracting the car model.
If you're going to make a skin you might want to bake a shadow layer too, but that's a very different procedure... ask google for it