The locks on your car are vacuum powered. There is no electric motors, switches etc...

If your key won't unlock the trunk then your best bet is to locate the vacuum line that goes to the trunk lock and simply apply vacuum to it with a Mityvac or similar. That should unlock the trunk (iirc there should be a vacuum connection in the passenger footwell)

If you don't have a mityvac then you can run a long vacuum hose from the intake manifold and apply vacuum that way

there should be 3 lines going to the back of the car:

1. Trunk locking
2. Trunk unlocking
3. Fuel flap locking

You will have to try them all probably until the trunk unlocks