Typical issue I've seen from many owners

Hi. First off thanks for the approval…
My issue and it appears many others, is.
My 06 jag S Type just started to give the left lamp tail light failure on the dash. I’ve tried every source of the people having the same problem…no success. I’ve changed bulbs, changed bulb holder, checked for grounding with meter, checked fuses, everything checks out. I’ve change so much so far frustration has definitely set in. Dont want to start spending unnecessary money for same result. I’ve had someone tell me to change out the battery…250 for no success…no way! Can someone who’s had this same problem tell me EXACTLY what solved this problem. Inspection time and no brake light isnt going to get it done. Thanks.