I'm not editing the car for my mod, but... There should be a script attached to it (it behaves like a party member). It should also create the invisible hex blockers (the stuff dictating where you can or cannot pass, every object huger than a hex has them). If the vehicle has a different size than the regular car a script should be present.
If the mod only contains .FRMs then simply copy/paste into data folder. If it also contains scripts then check if there are script.lst and script.msg: if they are not present you can simply copy/paste into data.
If the mod also contains new weapons/maps and the like then odds are you'll need the MOD runner. Bye.