It seems to me that all of Stephen King's books/films are connected, usually through small details. However, I do not know how the "classic" film Maximum Overdrive and the short story it was based on connect to the others. Are there any details found within these stories that serve as connective tissue, or are they simply standalone?
There is a connection of sorts: The movie Maximum Overdrive starts with this opening text:
On June 19th, 1987, at 9:47 A.M. EST, the Earth passed into the extraordinarily diffuse tail of Rhea-M, a rogue comet. According to astronomical calculations, the planet would remain in the tail of the comet for the next eight days, five hours, twenty-nine minutes, and twenty-three seconds.
As the Stephen King Wiki puts it, "19 is a mystical number that appears regularly throughout the works of Stephen King, particularly the Dark Tower series."
Moreover, June 19 (1999) is the date of King's car accident, which is also part of the novel The Dark Tower VII: The Dark Tower. But of course, this was in the future when Maximum Overdrive was made, so it's a coincidental connection.
By the way, the comet (and the date) are not mentioned at all in the short story, Trucks.
Well, the immediate connection that jumps out at me is that Trucks (and Maximum Overdrive) are about cars/machinery that have some sort of sentience. Haunted/sentient/evil cars (and other machinery) are definitely a "King-ism." The most obvious examples are Christine, and From a Buick 8, but IIRC there is a (semi-?)sentient soft drink machine in The Tommyknockers, (or was it Dreamcatcher?) and I seem to remember some evil intent imputed to the car in Mr. Mercedes. Actually, I just stumbled upon this article specifically about King's love of scary cars.
It has been a very long time since I have read Trucks, so there may well be other "King-ism" elements within the story that I simply don't remember.
But, knowing the history of the story, it would make sense that many of the typical "King-isms" are missing from this story. According to the Wikipedia entry for the story, it was first published in 1973 in Cavalier magazine. King's first novel, Carrie, was not published until 1974.
It might be that there are simply not many connections with other works because he didn't have any other works to connect to at the time he wrote the original story.
As far as I can remember - and my memory is pretty good - Trucks was a standalone short story. Other than using the fictional town of Castle Rock (with some shared characters) there was no "king-verse" until around the time of the third book of the dark tower series.
After that hints of the dark tower, and actual "dark-towerness", started showing up in various stories, Hearts in Atlantis, Everything's Eventual, Insomnia, and many more which pointed to a magnificent tying together of all these things.
However we didn't get that magnificent resolution (and I've no great faith that we ever will).
The Happy Toyz Truck has an evil clown face on the trailer doors. Pennywise from It reference maybe.