If I understand correctly, the two main tips that I think might help is to mask a larger graphic to only show within the perimeter of the vehicle outline (minus front windows and some door handles etc) ...and to give the graphic some transparency to allow a little of the vehicle detail or 3D qualities to show through from the template.
For masking, create a vector path defining the space to be wrapped on the vehicle. If that contour (or compound contour) is on the same layer as a graphic (which would be easiest if the graphic were a flattened rastor image for this process) & then selecting both, you would go to the object menu, choose "clipping mask", and then choose "Make".
Then to add transparency, just select the graphic, pull down the 'windows' menu, choose "show Transparency" and slider the "opacity" slider to whatever looks good.