Third stop light not working how do you replace it or find fuse on 2008 buick lurecene

'"Lighter Ports"? You mean accessory power outlets and cigarette lighters?

Fuses 26 and 31.

Buick Lucerne (2006-2011) fuses and relays

Fuse Box Diagrams https://fuse-box.info > buick > buick-lucerne-2006-20...

Cigar lighter (power outlet) fuses in the Buick Lucerne are the fuses ? F14 and F23 in the Rear Under seat Fuse Box (2006-2007) or fuses ? F26 and F31 in the Rear ...

2008 Buick Lucerne fuse box diagram

StartMyCar https://www.startmycar.com > Lucerne > Fuse box
The 2008 Buick Lucerne has 2 different fuse boxes: Underhood Fuse Block diagram. Rear Underseat Fuse Block diagram. Buick Lucerne fuse box diagrams change ...

Check engine light on ? Have it checked for DTC'S - diagnostic trouble codes . All problems maybe linked together . If you don't want to take to a qualified repair shop , auto part stores will check codes for free ,most will ! i hear advance charges $20 now. Third brake light may just be a bulb or the Stop lamp relay in the under hood fuse box.
Stop Lamps
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G302.

The 3rd brake light and the tow side lights are on different fuses, have you verified that they are both good. The other part that can cause this is the multifunction switch (AKA turn signal switch).

try all fuses for items you have described. Some fuses can grt brow on fuse leg post if so either clean or put new fuses in. its cheapest option to try first.

HARD CORE.....ELECTRICAL TROUBLESHOOTING....PERIOD! FIRST CHECK THE UNDER HOOD POWER DISTRIBUTION BOX FOR ANY BLOWN "MAXI-FUSES, OR CIRCUIT BREAKERS.
OTHER THAN THAT THE CONCEPT IS SIMPLE...THE FIRST PLACE YOU DETECT POWER, AND THE LAST PLACE YOU DON'T!
DO NOT JUDGE FUSE CONDITION ON "LOOKS" REPLACE ANY IN THE CIRCUIT

Stop Lamps
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G302.
Did you check the blub , is there power ( B+) at the third light ? Is the ground G302 good ? Do you have a DVOM - digital volt ohm meter , do you know how to use one ? Do you know what voltage drop is ? an know how to test it ? Check the stop lamp relay in the under hood fuse / relay box.
Did

If you have your owners manual it will be in there.

Third brake or stop Light.

I worked for a GM dealership,The problem maybe in the turn signal switch. The brake lamp circuit is wired into it to turn off cruise control.The third brake lamp is a circuit by itself.