off the top of my head, I think you will find that:
1.) the employer may require a harness in a (b56.1 standard) fork mounted maintenance cage, but the standard does not require any harness, as the fall protection is offered by the hip rails, mid rail, toe plates, positive locking gate, and guard on the mast side and the fact you are not permitted to climb on the sides of the cage.
2.) yes, at any time you are operating a man up order-picker, you must wear the proper fall protection, the height allowed before fall protection requirement was an older regulation that covered boom type man up lifts, but that reg (?A92.5-1996?) was changed in about 1996 to reflect that anytime the operator had enabled operation of the machine (on the dead man/operator in place pedal) that a full harness was required to be properly worn and secured.
What does the operators manual say?