The other day I discovered that my brake lights were acting up (inconsistently not working/and or flickering). After further investigation I discovered that when I have my lights off, this problem is reoccurring. Yet, when the lights are on the brakes seem to be fully functional. I observed the lights and discovered weathering in the rear passenger side tail light that is mounted onto the quarter panel. Water in the light itself and all over where the connectors are. I ordered another RH taillight for the quarter panel from a salvage yard nearby. Upon opening of the package I observed weathering in this tail light as well (oxidization, and some water). I installed the new taillight and when I tested the brakes, only the middle bar inside of the windshield would light up, none of the taillights would. Yet, when I turn my lights on again… all brake lights are fully functional. Any ideas?
Check the HAC Relay in the engine room relay box.
2012 Kia Optima Brake Lights Wiring Diagram