The wheellock has both a primary and a secondary sear. The knife on the kicker trigger strikes the secondary sear's arm which protrudes laterally from the lock, disengaging it from the primary sear. The tension of the mainspring on the wheel, once the secondary sear is out of the way, allows the primary sear to disengage from the wheel and the wheel rotates.
On my own pistol, my trigger is pinned through the stock ABOVE the plate, creating a very long trigger that consequently has enormous leverage. And the secondary sear is very easliy moved backward out of the way of the primary sear, so the trigger pull, even without a set trigger is extremely light.
Here's a picture taken right out of George Lauber's book, "How to Build Your Own Wheellock-Rifle or Pistol".
From what I can see in your photos, the front trigger is broken off just below the plate. So that trigger needs to be repaired or replaced. This trigger is a single action trigger and must be set to fire the lock. The front trigger cannot be used to fire the lock without first having been set. I suspect that's how it got broken...someone who didn't understand the system tried to release the wheel simply by pulling the front trigger, without first setting it.
