Continuity mistake: The outside view from the Bundy sliding doors/patio is different in the opening and most scenes from the shows. In fact, I can't think of any time it's the same.
Have You Driven a Ford Lately - S1-E5
Continuity mistake: Marcy gets two cans of soda for her and Peg to go with their salad. Camera changes shots and it's now two glasses of soda.
Poppy's By the Tree (1) - S2-E1
Continuity mistake: When Kelly walks over to the table, she burps. She breaks character by laughing with her head down yet a second later, she has a serious look on her face.
Poppy's By the Tree (1) - S2-E1
Continuity mistake: Bud asks to go down to the high school "tomorrow" to meet the man who met Andy Griffith. Earlier Al reads the events page in newspaper. The event was said to be "tonight."
Girls Just Want to Have Fun (1) - S2-E5
Continuity mistake: When we first see Peg and her friends at the kitchen table the fridge door is closed. Steve comes in with flowers and the door is open. He goes into the kitchen and it's closed.
Girls Just Want to Have Fun (1) - S2-E5
Continuity mistake: Al is having his fridge repaired. He goes and gets a beer and closes the door. A few shots later the door is wide open without anyone going near it.
Girls Just Want to Have Fun (2) - S2-E6
Continuity mistake: When sitting on sofa with Marci, Peg's necklace falls beneath her red blouse. It remains under in most shots, but in the last shot it is outside her shirt.
Continuity mistake: Marcy tells Peg that Steve has been gone for 5 days. Yet when he gets home, he has grown a full beard. It would take longer than 5 days to grow a full beard like that.
Build a Better Mousetrap - S2-E15
Continuity mistake: When Al hits his thumb with the hammer when trying to hit the mouse in the wall, he hits his left thumb. In the very next scene, Peggy is wrapping up his right thumb.
Continuity mistake: When young Al reaches forward with his left arm to take the book that Miss Degroot wants to give to him, she quickly pulls back but young AL still has his arm raised. In the next shot, his hand his down by his side.
I'll See You in Court - S3-E10
Continuity mistake: While they are in court, Steve is talking about the case and the clock says 12:30. Next time he's seen and talking about privacy to the jury, the clock says 11:30. Then when done talking, the clock says 3:00. The very next scene as the court proceedings are going forward, now the clock says 12:29. Next scene says 4:32. Than backwards again. The clock is moving forward and backwards throughout the entire scene.
Can't Dance, Don't Ask Me (aka Kelly's Dance) - S3-E13
Continuity mistake: During Kelly's dance, a nerdy girl grabs Bud and starts kissing him, but in the next shot, Bud is standing alone in the background. (00:20:30)
Can't Dance, Don't Ask Me (aka Kelly's Dance) - S3-E13
Continuity mistake: While Kelly is dancing with the guy at school, a nerd girl starts kissing on Bud and pushes him backwards. The very next second when the scene changes, Bud on the left side is back playing the record for the music without anyone around him.
Continuity mistake: When Kelly is at the grill, right after being called a "dullard" by Bud, Kelly grabs Bud's wrist with her left hand. As we pan out on the exact same scene, her hand is nowhere near his wrist.
Continuity mistake: Al takes the kids camping. When he leaves the house, his shirt is light blue. When he comes out from the bushes in the woods, it's dark blue with red stripes.
Continuity mistake: A lady agrees to buy some of Peg's red hair. It shows the lady with two baggies with red hair in them, but at the end of the episode we see that they used Buck's hair, which is far from being red in color, or anything like human hair.
Continuity mistake: When Kelly blows up the car near the end, when they show the car before it explodes, you see someone walking on the right side behind the car. Half a second later the car explodes and now someone is walking by the building on the left side of the screen. There wasn't anyone there before.
Continuity mistake: Kelly knocks the lampshade off the lamp. Next shot shows it put back on although no-one is around it.
Continuity mistake: Marcy's floral headpiece falls off during the backyard wedding scene, then, in the next shot, after she hits Al with her flowers, it appears on her head again. (00:18:30)
Continuity mistake: The out of order sign on the toilet changes position between shots. It's level at first. Camera cuts to other men. When it cuts back to Al it is tilted. (00:18:18)
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.