How to make rear deck electric latch work?

did you try going straight to the solenoid to see if it jumps at the wire? I would start at the solenoid itself and work back to the switch instead of the other direction. An open coil will not be detectable if you do not approach it that way. First use an ohm meter to ohm it out and then put the 12V to it to see if it kicks.. could be a stuck solenoid or open coil in the solenoid. Move back into the circuit once you verify that and into the fuse block as a halfway point. Remember, divide and conquer.