Well, perhaps Harry uses magic to fix cars in a really unique way. Like he might use a spell to make the engine parts float into place instead of using tools.
One idea could be that Harry is secretly working on cars to create a vehicle that can travel between the wizarding world and the Muggle world without any issues. He combines his wizardry skills with his new - found knowledge of cars. He might be using magic to disguise the cars as ordinary Muggle vehicles when needed, and then with a flick of his wand, transform them into magical cars with special abilities like flying or underwater travel for when they are in the wizarding world.
Ron could be there too. He might be more interested in the cool features of the cars, like the sound systems or the design. He could be the one who tries to convince Harry to add some fun elements to the cars they work on. And Hagrid might also show up, being all amazed by these strange Muggle contraptions and accidentally breaking something while trying to figure out how they work.
Perhaps Harry's interest in cars begins when he visits the Muggle world more often. He gets fascinated by the different models and mechanics of cars. He then starts collecting them with the help of his Muggle - born friends who know more about cars. In the fanfiction, he might even modify the cars with a touch of magic, like making the engine run on magic instead of petrol.
In some fanfictions, the cars are actually enchanted objects in the wizarding world from the very beginning. They are like sentient magical beings that have been hidden away for years. And then the Harry Potter characters discover them and have to figure out how to use them to defeat the dark forces. It's a really cool concept that combines the technology - like aspects of the cars with the magic of Harry Potter.
In this fanfiction, perhaps Harry Potter is brought into NCIS because there are rumors of a wizard - made weapon being used in crimes. He would have to navigate the non - magical world of law enforcement while also keeping his own magical identity a secret. His owl, Hedwig, could be used to send messages in a discreet way that NCIS could benefit from. He might also introduce some of his wizard friends, like Hermione, to help with research using magic - enhanced techniques.
Perhaps in this fanfiction, Harry Potter is recruited by the queen to solve some magical mysteries within the palace. He could use his knowledge of the wizarding world to uncover secrets that are plaguing the monarchy. For example, there might be a cursed object in the palace that is causing strange happenings, and Harry is the only one who can find and break the curse.
One interesting aspect is the characters' new roles. In 'Harry Potter races cars' fanfiction, Harry and his friends could be racing champions or mechanics. They get to show different skills and personalities outside of their normal Hogwarts activities. Also, the settings can be really exciting. Imagine a race track in the Forbidden Forest or on the Quidditch pitch. The races themselves are full of action, with spells being cast to speed up or slow down other cars. And the rivalries between different houses or wizarding families add an extra layer of drama to the story.
He might inherit some of the cars. For example, he could inherit a classic wizarding car from his parents' old friends. Another way could be that he wins them in magical contests. There could be a Triwizard Tournament - like event where the prize is a unique and powerful car.
Well, he might encounter a lot of dark and dangerous items. Maybe he'd come across illegal potions or cursed artifacts. He could also meet some unsavory characters who are into the dark arts.
One idea could be that Harry is in need of a job after graduating from Hogwarts and ends up in Gordon Ramsay's kitchen. Harry's quick reflexes from his Quidditch days help him dodge flying pans and utensils when Gordon is in one of his angry chef moods. He also uses magic to keep the kitchen clean, which impresses Gordon, and they start creating magical - infused dishes together.
Well, it could be that the ICW has a special task force to deal with emerging magical threats. Harry, with his skills and reputation, is recruited. He might be sent to investigate strange magical occurrences that seem to be connected globally. He'd have to work with wizards from different cultures and magical traditions, which would be a big challenge but also an opportunity for him to grow as a wizard.