Revealing mistake: When the truck is being pulled off of the bridge by the ship, if you look closely right before the truck plummets towards the water, there is no engine, transmission, or anything else in the engine compartment of the truck, which was left exposed after the hood fell off in an earlier wreck.
Revealing mistake: Right after the explosion, when Simon walks up to a detective and introduces himself as an adjuster for the bank, he asks if the detective can show him the way down. When the detective says yes he calls over an officer Murphy, who is facing the crowd. Murphy is already looking back and begins to walk to the detective before he is even called for.
Add timeRollin Garcia Jr
Revealing mistake: When they are being chased in the Mercedes, McClane tells Carver to pull the fuse for the anti-lock brakes. When Carver says he won't know which fuse is which, McClane tells him to pull them all. If Carver were to do this, he would cut electrical power to critical functions, such as the fuel pump or ignition system.
Revealing mistake: When Bruce Willis and Samuel L Jackson are climbing down the rope (or whatever it is) to get to the ship, the green Dodge falls off the bridge. If watch closely, you can actually see that the truck is tied by another rope in the back, which rips as the truck falls into the water.