Revealing mistake: After Station 51 is dispatched to the 'plane in trouble' it becomes a plane crash rescue and recovery, and when they pull out the pilot's body, who they said died on impact, his right hand moves to clasp his left wrist, and he also bends and moves his leg.
Smoke Eater - S4-E16
Continuity mistake: When Billy's mother waits in the hallway while Early examines Billy, the window behind her is on the same side as the ER's receiving entrance. Note that outside the window there's a blue metal shade at the top, which does not exist in any exterior shots of that side of the ER.
Transition - S4-E15
Continuity mistake: When Gil is assigned to ride along with Squad 51, en route to the incidents there are only two people seated in the squad in the shots shown.
Visible crew/equipment: After Chet's disappearing half-dollar trick, when Squad 51 is dispatched to the gunshot wound, as Roy and Johnny get into the squad numerous set lights are reflected on the squad's chrome spotlight.
Camera Bug - S4-E10
Visible crew/equipment: After Johnny tries to take Chet's picture beside the map, when Captain Stanley walks from the office to the back of Squad 51, the reflection of crew/equipment are visible on the back of the squad.
Continuity mistake: While Johnny tries to reach the man who fell over the cliff, when the bicycle falls to the bottom of the canyon both tires break free from the frame, but when the officer retrieves the bicycle, only one of the tires is off, the other is undamaged and on the frame.
Visible crew/equipment: After the rescue on the draw bridge, when Squad 51 gets back to the station Roy goes to the backyard and sits in the sports car, and in this shot just as we hear Johnny's footsteps, on the Land Rover's window we can see the reflection of a crew member who is moving backwards.
Continuity mistake: When John and Roy walk into the house with the pregnant gunshot victim, only John's wearing a helmet and he places it on the floor near the victim's husband, but in all of John's closeups (from the unusual POV looking up at him) his helmet is on the counter. Additionally, there are blue glasses upside-down on the side of the dish drainer, but in those closeups of John the glasses have vanished, and the glasses vanish again when Roy helps the husband get on his feet. Also notice that there's now a blue glass in the sink.
Visible crew/equipment: In the locker room, after Chet tells Johnny that he knew all about the practical joke, when they walk to the door together there's a quick glimpse of the cameraman's reflection on the door's glass, before John tells Chet about the fictitious five dollar bill down by Mike's locker.
Continuity mistake: There are only two ambulance attendants who take the pregnant gunshot victim to the vehicle, but en route we see two attendants in the front seat - driver and passenger, and a third attendant is in the back with John and the victim. Then when they reach Rampart, the attendant that was in the back with John has vanished and he's the one who opens the back door from the outside. As an aside, in the ambulance, when John talks to Rampart about fetal heart tones, we see the attendant is actually mucking around with the IV drip.
Visible crew/equipment: When Roy and John get back to the station, and Marco walks up to the squad to talk to the guys about the practical joke they're going to play on Chet, on the squad's spotlight we can see the reflection of the camera, which is in front of the map.
Daisy's Pick Blind Date - S4-E7
Continuity mistake: When John shows Chet the card with the address that Daisy gave him, Chet quickly takes John's pen to write the address, and when John grabs his pen back he quickly and unsuccessfully tries to put the pen back in his shirt pocket, but in the next shot the pen's in his pocket.
Daisy's Pick Blind Date - S4-E7
Continuity mistake: When John and Roy are with the little boy in respiratory arrest, while John uses the Ambu bag his watch reads 12:15, then he informs Rampart that they have O2 on the boy and goes back to the Ambu bag, and now his watch reads 12:25, though it's only been a minute.
Visible crew/equipment: When Brackett walks out of his office, Betty walks over to him and asks if it's okay to go to Dixie for help with the nurses' scheduling problem, and the bulging outline of the mic transmitter is visible on the back of her uniform, directly under its zipper.
Visible crew/equipment: When deciding how to rescue Cora from the middle of the cactus patch, Mike parks Engine 51 at the side of the road, beside the hill with the cactus. During the rescue there are closeups of Cora's husband standing beside Engine 51, and we see other things reflected on the engine instead of just the side of the hill. Additionally, his position in the closeups differs from where he stands in the wideshots.
Visible crew/equipment: When the guys are at the scene of the vehicle accident, after Roy asks Captain Stanley and Captain of 69 to assist the man to the top of the hill, the reflection of the array lighting is visible on the side of Engine 51 as Mike works the engine's pump panel.
Continuity mistake: When Station 51 is dispatched to 'vehicle accident with injuries', Roy is in the locker room still getting into his uniform with his shirt untucked and belt undone when re runs into the apparatus bay, but in the next overhead shot Roy's uniform is on properly.
Continuity mistake: When Chet and John are by the sink talking about Chet's appearance on the news, in the reflection we can see the three lockers behind Chet, and in the next shot the door of the fourth locker is wide open, blocking the third locker, and we can see that it's open because of the poster that's taped to the inside of the fourth locker's door.
Continuity mistake: After loading the officer with the gunshot wound onto the ambulance, en route to Rampart when Johnny is checking the wound, Johnny's watch reads 11:10, but when he's adjusting the mask and the resuscitator regulator, his watch reads 11:55.
Continuity mistake: After the sniper throws the rifle out the window, Captain Stanley gives the orders over the HT to Engine 12, Truck 23 and Engine 23, and the next few shots of the rigs are from previous episodes including 3x7, "Promotion", when Roy and John rescue the security guard at the structure fire.
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.