Brake light in trunk/spoiler out

you can use one of the wires from either brake light and make yourself a good ground in trunk and running the two wires to you light switch. be careful where and how you run wires around the trunk hindges as you do not want them to become pinched and short out as that is a safety issue and get you pulled over. always solder and heat shrink all splices and wire to wire connections, if you dont you will hate your self later as wire from front of car to back of car could then need to be replaced.

I’m happy to assist further over the phone at https://www.6ya.com/expert/christpher_f760d0f18f8eedc3

lift the car and lock inside of the spoiler turn the conector and pull out the light bulb and instal the new bulb light

have to trace back wires from the one thats working cos they are usually on same feed ,, ,, especially the connections to the spoiler ,,

Replace the turn signal switch. All of these lights run threw it.

There are usually two ways that these lights are mounted. One is under the light through the trunk. Another is just popping the plastic cover over the light off. It slides back. In some cars in others, it has a screw.

This is a simple bulb replacement.Simply pop off the access cover(if you need to) then twist the bulb in a counter-clockwise motion to remove it.Install is opposite of removal.I hope I could help, rate me accordingly, Thanks.

through the trunk you have to remove the trim material/trunk lining around the back of the light housings and remove the bulbs

I believe you pop the trunk and pull back the liner to access the bulbs from in the trunk compartment.

If the light in the spoiler works, the switch is good. Sounds like a bad ground to the light sockets

In the trunk, in the rear corners, you'll see some plastic "caps" with tabs on them, similar to wing nuts. Remove those, and the taillight comes right off the back of the car. That will allow you to replace the bulbs.