The third zone in Resident Evil 4 is the Island. Once again, Ashley has been kidnapped, and Leon has to free her. But, before you can do that, you'll need a Level 3 Keycard. Here's our Resident Evil 4 Keycard Access Terminal Puzzles guide to help you with this particular objective.
The Resident Evil 4 Keycard Access Terminal Puzzles guide takes place in the laboratory area of Chapter 13. Continue through the level until you reach the Merchant hub in the kitchen, which is connected to the lab hallway.
Lab area map.
Puzzle #1: Dissection Room - Level 1 Keycard
Go to the Power Control Lever and flip the switch. You may also unlock the nearby shutter gate so you can return to the Merchant's hub a lot faster.
Head to the Dissection Room, where you'll see a terminal. You'll notice several symbols, subdivided into sections. The goal here is to press the buttons so that each set of symbols will be rotated, forming an unbroken line from the "Power" source at the top-left, circulating to the two nodes with electricity icons.
For the first Resident Evil 4 Keycard Access Terminal Puzzle, we simply pressed the first two buttons (we ignored the third). After a bit of trial and error, you should have the same diagram seen in the image below. Press the fourth button to unlock the door.
The solution to the first puzzle.
You can then pick up the Level 1 Keycard that's on a table in the Dissection Room. However, when you attempt to exit this area, a Regenerador will spawn. These enemies are unnerving, as they're nigh unkillable since they'll flop around and regenerate their body parts. At best, you could shoot your foe in the head to stun it for a couple of seconds, but you should definitely run away or parry its attacks.
