hi and welcome The brake light is on the outside there are 2 plactic covers turn counterclock wise 2 torx bolts you need to remove pull to side . if you have any further questions let me know.
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The system works on resistance so if you have a new bulb and old bulb then it reads it as beiing out. try replacing bulb on other side. the other common problem is the rear wiring lite harness but the only fix is to replace harness.
the same to you