[Vince]

Personally, I use 3D Studio (GMax should work too) to find the exact coordinates, as it allows me to zoom in and view the object from every angle. Just keep in mind that the origin (0,0,0) is the center of the car and that you should picture the car from its rear.

If you want to move the object to the front of the car, increase the Y values. If you want to move it to the rear, decrease the Y value. Decrease the X value to move it to the left. Increase the X value to move it to the right. Increase the Z value to move it up. Decrease the Z value to move it down.