Norm,
The cab lighting typically has three open or closed sources for cab lighting power.
First; The building breaker panel marked CAB LIGHTING or something like that.
Second; In the elevator equipment room, there will be yet another switch mounted on the wall or on the elevator control cabinet hopefully marked CAB LIGHTS.
Third; Inside the cab, there should be a switch marked “LIGHTS/ON/OFF. Be sure all sources are ON. If still nothing, I’m not sure what to tell you but it needs to be determined if power is actually getting to the cabin, and at that point I suggest you get in touch with a licensed elevator company. However if you’re the licensed mechanic, then it’s up to you to figure it out, and it isn’t that difficult. Cab power sources, if absent, and all indications are there should be power, are the building owners responsibility.

Good luck.