After Michael Myers died at the end of Halloween II (1981), the plan by John Carpenter was to make a new "Halloween" movie each year, each telling a different Halloween-related story. After this movie underperformed at the box office, the film-makers decided to bring Michael back to life for future sequels.
A novelization of the film was published in 1982 by science-fiction writer Dennis Etchison under the pseudonym Jack Martin. Despite the film's critical failure, the book became a best-seller and was even reissued two years after the film's release, in 1984.
(at around 28 mins) When Challis fills in the register at the motel office, he scans the list of names for evidence of Ellie's father's stay. All of the other names on the list are the names of the crew.
Supposedly, part of the genesis of this film came from a comment made by film critic Rex Reed. Reed panned Halloween II (1981), saying it was so bad that, "If they make a Halloween III, I'll turn in my press card."
The film's original director, Joe Dante, approached Nigel Kneale to write the film while Kneale was temporarily living in Hollywood writing the remake of Creature from the Black Lagoon (1954) for director John Landis that was never made due to budget cost. Dante wanted a new and different story than the two previous films in the series, so he suggested Kneale write a treatment around the word Halloween. The producers liked the idea, and after Joe Dante moved on to another project, producer John Carpenter's regular collaborator, Tommy Lee Wallace, came in as the new director. Kneale initially blamed the drastic changes to his script on executive producer Dino De Laurentiis not understanding his dialogue when it was translated to Italian. Kneale requested his writing screen credit be removed once his comical mystery screenplay was rewritten by an uncredited Carpenter, and then later Wallace (who received sole screen credit as writer), to include more gore and simplify the story.
In an interview with the Pittsburgh Press newspaper shortly before the film's release, Tom Atkins told the hometown publication that he didn't know how the movie was going to end because they "shot a couple of different endings".
During a reunion panel for the cast and crew of the movie in the Summer of 2015, Tom Atkins and Stacey Nelkin confirmed that the bedroom scene was one of the very first things that they shot together. Both found it humorous because Nelkin had been quickly cast as Ellie Grimbridge due to time restraints on the studio's part and the two had barely gotten acquainted beforehand.
The Silver Shamrock theme was played a total of 14 times in the movie: four times at the gas station, once at Linda Challis' home; once at the hospital, once in the bar, twice on the television screens in the shop window, twice on the radio, once in the motel office, once in test room A, and once in the final admittance area.
(at around 1h 16 mins) When Cochran talks to Daniel in the holding cell, he mentions the ancient Irish holiday, Samhain. The sacrifices referred to by Daniel are references to the Pagan tradition rituals that were developed in the early stages of the ancient holiday. Cochran says he based his plan on the ancient holiday of Samhain. Many of the customs associated with the Halloween holiday have their roots in Samhain.
(at around 21 mins) You can hear the voice of Essex Smith, the actor who plays gas station attendant Walter, as the play-by-play commentator of the baseball game Challis is watching in the bar when Ellie finds him.
(at around 24 mins) The plaza where Challis called his ex-wife on the pay phone to shirk his parental responsibilities was also featured in Halloween II (1981) when Darcy is trying to get Karen to keep her promise of taking her home.
A Silver Shamrock jack-o-lantern mask with a silver clover decal on the back can be seen in a 1984 episode of the series Knight Rider (1982) (Knight Rider: Halloween Knight (1984)). Halloween III: Season of the Witch and Knight Rider were both distributed by Universal Studios.
The "Big Halloween Three"- the Silver Shamrock masks that are ceaselessly advertised in the movie- consisted of two altered masks that were already in the Don Post Studios' repertoire (the skull and the witch) and one made exclusively for the film (the jack-o'-lantern). The company was sold to Pennsylvania-based business Paper Magic Group, Inc. just before they were planning on re-releasing the masks to the public during the 2012 Halloween season. However, the rights were bought by California-based company Trick or Treat Studios and replicas of the original have been available to the public since 2014.
(at around 8 mins) When Walter (the gas station attendant) is looking over the rain after the power went out and he hears loud noises, the calendar on the wall is displayed on October 1982. The film was released in North American theaters on the 22nd of that period.
Interestingly it was the opening sequence of one of the films written by prolific British Sci-Fi writer Nigel Kneale, the man who retracted his contributions to the script of Halloween III, that inspired John Carpenter's iconic opening of the first Halloween film. It was the intro of the 1967 film "The Quatermass and the Pit", part of a trilogy and based on a popular character that Kneale created that turned the initial sequence from a sidewalk pan ending on a mask to the close-up pumpkin and extinguished light.
Executive producer Irwin Yablans was against not using Michael Myers in this sequel. He has said in interviews he had little to do with the finished film, and basically received credit for his minor involvement. He also said he did receive a "fat cheque" for his trouble.
The ONLY time in the film that the Rose of Shannon motel office light goes off is when Challis enters the premises to contact the authorities after the factory tour- possibly a visual cue for the suited men to kidnap Ellie. When he leaves the office, the light is on again.
In the Rose of Shannon motel registry, Harry Grimbridge noted the location of his shop as an address in Sierra Madre. The bar that Ellie finds Challis in and the shop with the televisions in the window were located there in real life.
(at around 26 mins) The Shamrock Savings Bank that Ellie and Challis respectively drives and walks past in the movie was (and still is) indeed a bank, the institution fittingly named after the town where the scenes were shot: Loleta, California.
(at around 25 mins) The farmer that Ellie and Challis passes on the way to Santa Mira was wearing a John Deere hat. Deere was an inventor who used his blacksmithing skills to create commercially successful agricultural machinery still in present use.
Based on Challis' ingenious attack on Cochran's henchmen in the final admittance area it can be determined that the Stonehenge-implanted trademark chips, combined with the Magic Pumpkin, does not have the same effect on robots. Little Buddy Kupfer's head became a deadly mass of insects and snakes- the robots were stunned and deactivated.
The trivia items below may give away important plot points.
at around 1h 30 mins) A special platform was built for the scene that shows the robot Ellie Grimbridge's head poking out of the ground next to her body. The scene was done by having Stacey Nelkin stick her head through a hole in the platform while a body double wearing Ellie's clothes stuck her head down another hole on the platform.
Marge Guttman's body was not discovered for almost four hours after the misfire. When Challis and Ellie are lying in bed just prior to Marge's tampering of the chip behind the company trademark, the analog clock face says 10:10. When they are awakened later by the sound of the factory vehicles driving up to the motel, the clock says 1:50.
Cochran and his "loyal and obedient" robots stole one of the stones from Stonehenge in January of 1982, according to the news report that the gas station attendant is watching at the start of the film.