In the scene when John Candy gets in the tanker truck carrying rocket fuel look at the two headlights on the truck. They are both in good working order. Then as the truck pulls out it starts to smash through cars damaging the 1 headlight. A little while later you see the truck come around turn to the right and both headlights are in good condition again. Then just before the truck gets blown up the trucks light is smashed again. It looks like when they filmed the movie they filmed the truck first being chased with good headlights. Then they filmed the truck before it started smashing the cars again still good headlights. Then as the truck smashed through the cars the headlight got damaged. Then some more chase scenes with the damaged lights were filmed. When the film got edited they put the chase scene with the good headlights in after the truck smashed through the cars. This creating the good to damaged to good and yes once again back to damaged.