i have a 71 chevy pu, and i was wondering how to lock the door when i get out without using the key. for some reason the door will not stay locked when it is shut. on the previous body style 60-66 i know that you push the door handle down before you shut the door and it will lock,ive tried holding the button in too. i have been looking around, and havent been able to figure it out. on these years is the key the only way to lock it????