The park brake lever has no tension on it and nothing happens at all when it is moved.
I use the override on the dash - otherwise the truck doesn't get above 20 mph. with the override on, I can get to 55mph... my thought was brakes were locked up.
I don't know what caged brakes look like - but will google it.
The parking brake handle works two different brake systems, the mechanical driveline brake which is cable operated and the spring brakes which are air operated.
If there is no tension on the handle then there is an issue with the driveline brake. The cable could be broken or have too much slack, the pads could be worn, the return spring could be broken or various other things. 95% of the tension on the handle is from the return spring and cable on the driveline brake. The rest is from the little spring on the spring brake actuator which most likely wouldn't be felt. Try tightening the knob on the end of the parking brake handle to see if you get any tension.
If the override button on the dash is applying and releasing your spring brakes I would suspect, as did 98G, that the actuator on the parking brake handle is the problem. You are trying to apply the spring brakes with the override button pulled out, correct? If it is pushed the parking brake handle will not apply the spring brakes.
I also agree, you need to sort this out before you put it on the road again. The override button on the dash is only used for testing. It is not used during normal operation. Push in the override button to independently test the driveline brake using the parking brake handle. Pull out the override button and raise the wheel on the spring brake actuator to independently test the spring brakes, without using the parking brake handle.