This could be the plastic piece on the the brake pedal that activates the brake light switch. Mine fell apart and kept the brake lights on until my battery died. I ended up using a panel retainer I got from Autozone. I bought the assortment pack (Dorman 963-075). If I remember correctly, the one I used required Channel Locks to snap in, but I know for a fact it won't fall out. After you snap it in, you may have to adjust the switch so it makes good contact.