The Wedsworth-Townsend Act - S1-E1
Visible crew/equipment: After Gage learns of the death of his last rescue, when he leaves the ER treatment room and passes the wife and daughter, the actor's black tape mark is visible on the floor, at the wife's feet.
Visible crew/equipment: When Dr. Bracket and Dixie begin to explain to Jenny that she was only hyperventilating, as she sits down in the wheelchair, the actor's tape mark is visible on the floor by the door, just before Dr. Bracket walks over and stands on it.
Visible crew/equipment: When DeSoto calls Gage to where he found the dog, the two actors' tape marks are visible on the floor when Gage sits on his bed.
Visible crew/equipment: Station 51 responds to a building collapse with the trapped boy, and when they enter the building with Tommy's friend, the actor's white T-mark is visible on the floor.
Visible crew/equipment: When Dr. Bracket leaves the treatment room with Jenny, who's being wheeled in the wheelchair, he tells her to see her family doctor just as Dixie exits the door, and the shadow of the moving boom mic is visible on the wall, at the top to the left.
Continuity mistake: Just as Gage and DeSoto walk into Rampart's staff lounge, while discussing practical jokes, DeSoto is holding the handy-talkie in his right hand, but in the next shot the handy-talkie has vanished.
Visible crew/equipment: When Gage and DeSoto are stuck cleaning the squad again before The Inspection, Captain Stanley walks in and the actor's T-mark is visible on the floor just before he steps on it. Additionally, when Stanley walks away, and Chet catches up to him, another T-mark is visible on the floor near the doorway.
Loose Ends - S6-E12
Visible crew/equipment: At the hospital, when Gage sells the picnic tickets to Dixie and Dr. Early, just as Dr. Brackett walks up to the nurses' station, both Brackett's and Johnny's T-marks are visible on the floor.
Visible crew/equipment: At Rampart, when Dixie walks over to Dr. Brackett, who stands behind the station, the tape mark is visible on the floor, just before she steps precisely on it.
Continuity mistake: When Christy walks into Station 51's kitchen, the bag strap is on her shoulder, but close-up it is gone, only to be back next shot when she removes it a moment later.
Continuity mistake: When Squad 51 is dispatched and headed to their destination, interior shots looking out the windshield are shown. It is only in these shots that the Dodge truck's red hood has vents on its right and left sides. There is no such thing in any exterior shots of Squad 51. The hood's style also changes.
Continuity mistake: At the stationhouse, when DeSoto and Gage are discussing the detective, in the shots facing Gage, DeSoto holds a cup of coffee in his hands, but in the shots facing DeSoto his cup is on the table.
Continuity mistake: When Gage plays the new game of poker with Kelly, the entire left side of the table is visible as the two begin. Next shot, DeSoto is suddenly sitting at that end, with an additional cup and saucer, opposite Kelly and Gage.
Continuity mistake: During the first two seasons of the show, when Engine 51 and Squad 51 are dispatched, sometimes one or both vehicles change their appearance when they leave the firehouse, while en route, or when they reach their destination. Note the hood, lights, etc.
Revealing mistake: When Squad 51 is dispatched from the stationhouse, the exterior shots show buildings, traffic, trees, etc., they pass along the way. In some close-up shots of Gage and DeSoto while en route, too much of the vehicle's left and/or right sides are visible, which actually shows nothing but a blank screen behind them.
Continuity mistake: The shaving foam on DeSoto's face changes between the face-on shots and the reflection shots, and in the reflection he shaved from cheek to chin, but in face-on shots only to the neck.
Revealing mistake: When Johnny and Roy are in the squad heading to Rampart after freeing the girl's toe from the bathtub, they get dispatched to 'possible electrocution' and we can see the white tape with "Kevin" inside Roy's helmet. (00:37:30)
How Green Was My Thumb? - S3-E17
Revealing mistake: When Roy brings the man with a laryngeal obstruction into the ER and is taken quickly to treatment 1, his head is tilted back and Early places a laryngoscope into the patient's mouth and says that he sees the obstruction. The problem is that we can see that the laryngoscope is actually at the side of the patient's face. Then, when Early uses the forceps to remove the obstruction, once again we can see that it does not go into the patient's mouth.
Visible crew/equipment: When the boy who was shot by a pellet gun is wheeled into the treatment room, at the start of the next shot there is a closeup of the domed surgical light fixture, which provides a reflection of crew and equipment, albeit upside-down.
Continuity mistake: While Charlie is finishing up on the squad's engine, Captain Stanley hands Johnny the address in the canyon that has overgrown weeds, and when Johnny packs up the toolbox, Charlie holds out the roll of electrical tape and the combination wrench, with its open-end up. However, in the next shot the only thing Charlie holds out is the wrench, but with its box-end up.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.