I only have a '88 560sl as reference and on this vehicle the trunk lock cylinder connection to the lock tang is pure mechanical, turning the cylinder to full clockwise with the master key will engage the tab to open the trunk. This mechanical movement will trigger the vacuum thus making no vacuum required for the lock at which you have inserted the key.

However, if your's is somehow different and requires power, connect jumper cables to the power junction on the right front fender. That should apply power as though the battery were charged.