The lock on the hatch operates using air pressure just as the doors and fuel filler cover do. They are not electrically operated.
This is a roadster Dave, there IS an electrical lock also, the one pizzaguy highly recommends disabling by removing the plastic tip from the plunger.
It is controlled by the top module to lock the trunk during top operation, in case the owner is stupid enough to try opening it while the top is in motion.
On second thought, not the owner, he/she would have to be in the car holding the button, I guess it's for stupid spouses or kids.
( unless you have the one-touch top mod, then you could display your stupidity by starting the top and rushing around to open the trunk ! )