This version of the semi was only briefly seen at the very end of the Pilot. The correct GMC General cab is used, and we believe this is the same Dorsey drop trailer used throughout the series, but with a very unique, mostly gold paint job.
Now the semi is starting to look closer to what we all remember. When the new Executive Producer, Robert Foster, came in at episode 13, "Hearts of Stone", one of his first mandates was to paint the semi black. This is the only episode to feature this unique paint scheme, where the triple gold pinstripes don't angle back up near the back of the trailer, and the gold chess piece insignia is much smaller. Footage of this semi, despite it only truly appearing in this episode, will appear throughout the rest of the series.
This is a blink-and-you'll-miss-it version of the semi. During the opening credits of "Give Me Liberty...or Give Me Death", K.I.T.T. is pulling into the semi at night. Notice the trailer's pinstripes are the same as Version #3, but the chess piece logo has been crudely painted over, no doubt in preparation for the paint job it's about to receive.
Finally, the semi receives the paint job that it will keep throughout the remainder of the series. The stripes now angle up toward the back of the trailer, and the chess piece insignia is much more prominent. This trailer is first featured in "Give Me Liberty...or Give Me Death".
Beginning with the third season premiere, "Knight of the Drones", the semi receives an upgraded cab, with a black sleeper added. This is actually a completely new cab. Note how the fuel tank is now situated below the door, where the original version, it is set back on the frame. This is the final version of the semi, used until the end of the series.
And while we are at it, the semi did appear in a few non-Knight Rider productions:
January 22, 1985: Street Hawk - "Vegas Run"
October 12, 1985: Airwolf - "And a Child Shall Lead"