Loose Ends - S6-E12
Continuity mistake: When Roy and Johnny are driving to the hamburger stand and stop to have a look at the squad's fanbelt, in the interior shots Roy is wearing his watch while driving, but when he exits the squad the watch has vanished.
Smoke Eater - S4-E16
Continuity mistake: After Dr. Early is called a miracle worker and then again tries unsuccessfully to get the apple from the machine, it cuts to Squad 51 pulling backwards into the apparatus bay, and the engine we see parked in the bay is the Crown from the first two seasons, not their current Ward LaFrance.
Continuity mistake: When Roy and John leave the ER after the baby delivery, the base station dispatches them to the motorcycle accident, and in the next shot as the squad turns the corner, there are three people in Squad 51, we see Roy, Johnny and someone seated between them, while they're en route.
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.