Revealing mistake: En route to the pick-up truck hanging from the freeway on-ramp, there is a flipped shot of Engine 51 and Squad 51 as they drive under the freeway before the camera pans in towards the car. Some giveaways are the reversed '51' on Engine 51 and the reversed 'road construction ahead' sign.
Visible crew/equipment: After Gage and DeSoto climb the ladder to get the dog off the roof the second time, when it cuts to Rampart there is a man waiting outside the treatment room, and the actor's tape mark is visible on the floor, at his feet.
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.