Factual error: The entire plot is based on the idea that they're going to steal $140 billion worth of gold. At a gold price of $300/ounce, that's 14,500 tons of gold - how's the suspension on those dump trucks? There's no way trucks like those could carry over 1,000 tonnes each, but Simon tells McClain there is $13 billion worth of gold in the back of McClain's truck.
Continuity mistake: In the beginning, when the big explosion occurs, watch the 2 last shots. Close shot from two blocks away: Big traffic jam. Wide shot from above: Half of the cars have disappeared from the same spot.
Continuity mistake: When Samuel L Jackson is at Yankee Stadium, there is a close up shot of him and in the background you can see the water hose used by the grounds keeping crew. Moments later, when the camera is on a further shot, you can see that the hose is gone. (01:20:50)
Revealing mistake: When fighting with Targo on the boat, McClane pulls a chain, which trips Targo over. When we see Targo being tripped from above, you can see it is a stunt double - not only is he bigger than the actor playing Targo, but also his hair is grey unlike Targo's brown.
Factual error: The security guard at the vault door fires a few shots from his handgun (about 6) down the hall towards Simon and the other terrorists. He then loads one of the shotguns and calls for help. After finding that the front guard was a terrorist he fires 14-15 rounds from the same shotgun before he is killed. The problem is that it was a Remington 870. Like most shotguns that size they only hold 8 rounds, or 9 if one is chambered.
Factual error: Typical for action movies. Willis and Samuel L. Jackson couldn't have possible survived the explosion of the ship being in the water or not. If the heat didn't get them the pressure wave would have.
Continuity mistake: After McClane hits Targo with the chain and knocks him out, McClane searches him. Targo's body is not only in a different position, but the chain is wrapped around his head, which McClane never did.
Other mistake: When John and Zeus are being chased by the German guys in the car, John asks Zeus to pull out all the fuses in the fuse-box. The next shot is a quick shot of the speedometer etc. and it is lit up. Surely if all the fuses were out it wouldn't be lit?
Continuity mistake: In the car chase scene where the Germans are in the Dodge Ram and Zeus and John are in the car, during the mid point of that scene you'll notice the ram has a hood, and a few seconds later it is missing it.
Continuity mistake: While in the police station, a chubby guy brings the suitcase with the liquid bomb and to explain how it works he dips a stick with the liquid and throws it away to make it explode. Watch now the guy behind him covering his hears: Headset off, then he puts it on; then suddenly, in a very brief shot, when he is behind the chubby man, the headset is off again. In the next shots he has it on.
Revealing mistake: When Charlie (the bomb technician) hears that there are still children in the school, he continues trying to disarm the bomb. Pay attention to the shots of the countdown timer. It goes straight from 1:01 to 0:59. There is no 1:00.
Continuity mistake: In Harlem, when Zeus gets his arm cut by the black dude wielding the switchblade, another black dude is swinging the bottle toward McClane's head-with his left arm. The following scene, McClane gets his head injured from the same bottle wielded by the same dude-only this time wielded by his right arm not his left.
Continuity mistake: When the police van leaves McClane semi naked on the street, his beard is a mere shade. When he mets Zeus, 10 minutes later, his beard has grown much larger.
Continuity mistake: When the police get to Chester A. Arthur school and the kids are all in the auditorium, we see Detective Lambert walk into the auditorium wearing no badge in his jacket pocket. In the very next shot, he is wearing it again.
Continuity mistake: There is a big stain of wet blood on the back of Zeus just after McClane burns the cuffs to escape from the bomb on the ship. When they run outside the stain is dry, smaller and blurry.
Deliberate mistake: When McLane pulls out the phone he shot up after he and Zeus get into the Yugo there are a lot of coloured long curly cables hanging from the damaged phone. Mobile phones of this era would not have had any of these cables inside them, it is a deliberately made prop.
Continuity mistake: During the car chase between the Ram and the Mercedes, the Mercedes is going around a red Plymouth Acclaim, but in the very next shot it is a Chevy Cavalier. The Ram truck then starts scraping between the wall and the other side of the Cavalier, but when it cuts to a close-up it is now hitting the side of a grey Buick that was in front of the Cavalier.
Revealing mistake: When the water is pushing the truck in the aqueduct, one scene shows McClane on top of it. The truck and McClane are a different color indicating they were superimposed into the shot.
Continuity mistake: When they're on the bridge, trying to find a way onto the barge and they first get out of the truck, the skies are very overcast, as shown by the rain on the bridge. When they cut away and cut back to McClane, the sun is now out and very few clouds in the sky. It's fairly obvious that it was shot on different days and the bridge watered down.
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.
Suggested correction: No, the car would interpret missing fuses as blown fuses and would display a light to highlight the error.
GalahadFairlight
In German cars, the lid of the fuse box shows a table listing the purpose of each fuse. The engine control unit, fuel pump and the dashboard also have fuses that you should avoid to pull.