From Dusk Till Dawn

Fugitive bank robbers and brothers Seth and Richie Gecko are fleeing the F.B.I. and Texas police. During the first few minutes of the film, they hold up and destroy a liquor store, killing the clerk and a cop. Two witnesses they held hostage in the store escape during the shooting. They still hold a bank clerk hostage in the trunk of their car, whom Richie later rapes and murders.
The Fuller family â Jacob, the father and a pastor who is experiencing a crisis of faith; his son Scott; and daughter Kate â are on a vacation in their RV. They stop at a motel and are promptly kidnapped by the Geckos, who force the Fullers to smuggle them past the Mexican border. Seth and Jacob make an uneasy truce: if the Geckos can make it past the border, Jacob and his family will come out of the ordeal unharmed. They arrive at the "Titty Twister", a strip club in the middle of a desolate part of Mexico, where the Geckos will be met by their contact Carlos at dawn. The Geckos demand that the Fullers have a drink with them before leaving, despite Kate's obvious discomfort.
Soon after entering the club, chaos ensues as the employees and strippers are all revealed to be vampires. Most of the patrons are quickly killed, and Richie is bitten by the star stripper, Santanico Pandemonium, and bleeds to death. Only Seth, Jacob, Kate, Scott, a biker named Sex Machine and Frost, a Vietnam War veteran, survive the attack. The slain patrons â including Richie â then come back to life as vampires, forcing Seth to kill his own brother.
During this second struggle, one of the vampires bites Sex Machine in the arm. Subsequently, Sex Machine changes into a vampire and bites Frost and Jacob before Frost throws Sex Machine through the door, which allows an army of vampires to enter as bats from the outside. Seth and the Fullers desperately escape to a back storeroom and fashion anti-vampire weapons from items found therein, including a pneumatic drill, crossbow, shotgun, and holy water, which requires Jacob to recover his faith to bless. Jacob, knowing he will soon turn into a vampire, makes a reluctant Scott and Kate promise to kill him when he changes.
The four make their final assault on the undead. Jacob changes, but Scott hesitates to dispatch his father, allowing Jacob to bite Scott. Scott hits Jacob with holy water and shoots him. Scott is captured by several vampires who begin to devour him. Begging for death, Scott is shot by Kate. Only Seth and Kate survive, surrounded by vampires. Just as they contemplate suicide, streams of sunlight shine through new holes in the walls, making the vampires back away. Dawn has come, and Carlos is trying to shoot his way in. On Seth's call, Carlos' bodyguards blast open the door, letting in full sunlight and killing every vampire inside. Carlos admits that he had never entered the club, but that he had thought it looked like "a fun place."
Kate asks Seth if she can go with him to El Rey, Mexico, but he declines, saying, "I may be a bastard, but I'm not a fucking bastard." They go their separate ways after Seth gives Kate some cash. As they leave, the camera pans back to reveal that the "Titty Twister" was actually the top of a partially buried ancient Aztec temple, presumably the home of vampires for centuries, and that hundreds of vehicles have been toppled down the side of the cliff.

Question: What caused the vampires to back away from Seth and Kate?
Answer: Sunlight