Factual error: The electric guitar Marty plays at the "Enchantment Under the Sea Dance" is a Gibson ES345. This guitar model debuted between 1957 and 1958 yet he's supposedly playing it in 1955. It would have been more accurate to have him using a Fender Telecaster (1950) or Stratocaster (1954) or a Gibson Les Paul (1952). (01:23:50)
Factual error: When Biff is chasing Marty (on the 'skateboard') around the Town Square, you can see curb cuts at the corners. Aside from a trial program in Kalamazoo, Michigan in the '40s, they didn't spread further until well after 1955. (01:05:58)
Factual error: When Marty hits his head on the DeLorean's steering wheel, the car's horn honks. This is inaccurate to the design of real-world DeLoreans, as a DMC-12's horn button is actually located at the end of the turn signal lever rather than in the steering wheel. (01:39:27)
Suggested correction: You can't see his left hand and he could have accidentally pushed it when he hit his head. Or Dr. Bown customized the steering wheel so the horn is in it, like he customized the entire interior of the car.
I thought the point was that the car was so unreliable that when hit his head on the steering wheel, the horn went on. Makes sense to me. I own a DeLorean by the way.
Factual error: Marty McFly goes back in time to visit his mum-to-be and finds her watching an episode of The Honeymooners. The date is given as November 5, 1955 and yet the episode of the show - The Man From Space - was not screened until December 31, 1955. (00:44:15)
Factual error: When Marty walks out of Lorraine's house, next to the front door is a light dimmer switch. Dimmer switches weren't invented until the late 1950s to early 1960s. (00:47:34)
Factual error: Video/audio output on the JVC camcorder (if it had any at all) would not be compatible with 1955 TV. if available the camcorder output would be composite, component or COAX - all would need some sort of adapter for the audio/video to work on the TV. COAX would be the simplest, but they would need to invent the 75 ohm to 300 ohm adapter.
Factual error: In the skateboard chase scene, after the crash, a crowd gathers. In this crowd there is a kid dressed in a Cub Scout uniform. He has a red/white town strip patch on his arm. In 1955 the Cub Scout town strip patches were blue with gold lettering. (01:07:48)