This is a picture of the KZ-900P, it's used in season one and season two.
The KZ-1000P is used from season 3. It has a different windscreen, other front fender, smaller pursuit lights and other (small) changes.
They used the same trailler from season 3 as they did in the first two seasons. The bikes on the trailers were KZ-900P and those had the big pursuit lights and other windscreen. Because the diffence would be visible, they "reengineerd" the KZ900. They removed the KZ900-P windscreen and put a KZ1000-P windscreen on the bikes. They forgot to replace the pursuit lights (they are still the KZ900 lights), so they are much bigger than the lights which are on the KZ1000. Also, the metal frame below the headlight is missing on the KZ900. See this (rare) picture:
Erik Estrada owns one of the KZ-1000P bikes which was used in the series. Note that the engine was taken out.