If a vehicle pulls up to a player, the player can rip the contents from the cargo, specifically the parts needed for the vehicle (Battery/glowplug) - simplest constraint IMO - Require the bonnet/hood to be open to remove the car components (glow plug/ battery).

Would be nice to get this constraint in as early as possible - allowing such a difficult/rare item to acquire to be lost with such ease and complete discretion (if the thief is smart enough (has the inventory space)) will obviously become a fairly frustrating issue for some.