The dashboard is a standard component of the Weasleys' turquoise Ford Anglia, a Muggle car. Its most significant feature, added by Arthur Weasley, is a small, unlabeled silver button. This button is the control mechanism for one of the car's most powerful enchantments.
The dashboard's primary magical function is to operate the Invisibility Booster of the enchanted Ford Anglia.
The dashboard was originally a mundane part of the Ford Anglia that Arthur Weasley procured. Driven by his fascination with Muggle artifacts, he illegally modified the car, adding enchantments for flight and invisibility. He discreetly installed the silver button onto the dashboard as the manual control for the Invisibility Booster, keeping his modifications a secret from both the Ministry of Magic and his wife, Molly Weasley.
The dashboard and its invisibility button are featured prominently in Harry Potter and the Chamber of Secrets. When Harry Potter and Ron Weasley find themselves barred from Platform Nine and Three-Quarters, they decide to fly the enchanted car to Hogwarts. Shortly after takeoff, Harry notices the silver button. Ron identifies it as the Invisibility Booster and presses it, concealing them from Muggles below. The subsequent failure of the booster during their journey creates significant tension and directly leads to their violation of the International Statute of Secrecy, as they are spotted by several Muggles. This incident results in a disciplinary letter for Harry and Ron, and a formal inquiry for Arthur Weasley at the Ministry of Magic.
In the film adaptation of Harry Potter and the Chamber of Secrets, the dashboard's design is more elaborate than described in the novel. The control for the Invisibility Booster is depicted as a large, clearly-labeled toggle switch rather than a small, nondescript button. (film)