Okay i actually found the cable (after looking in EVERY room in the saylum) ! But 2 things are confusing me :
1. I'm still missing a secret in the asylum as mentionned before. (Found it).
2. In the secret pathway near the reject's lair (which leads to a skull) there is a card reader head that i can't use. Does that mean i need another card or is it just for decoration ? I'm asking because i'm pretty sure it wasn't there in the main game.