A seat belt retractor latch solenoid is integral to each of the two outboard front seat belt retractors. The solenoid is grounded at all times through its wire harness connector and circuit. The solenoid receives battery current, which is switched by the Seatbelt Control Timer Module (SCTM), through a fuse in the junction block.
When the seat belt retractor latch solenoids are energized the retractor spools are unlatched, and the seat belt webbing can be withdrawn from the retractor. When the solenoids are de-energized the retractor spools latch, preventing the seat belt webbing from being withdrawn any further from the retractor.
So, can you apply 12 volts to this solenoid and see if the solenoid will release the belt. If it won't, then the seat belt retractor needs replacing.
I hope this information is helpful and let me know if you need further assistance with this.