Left rear taillight not working
 

The driver side taillight won't come on. I've checked/changed the bulb and still no help. I tried looking for a blown fuse but there isn't one for just that.

Anyone knows what the cause of the issue? What can I do to test it?

This has happene to both of my lights the harness isn't that great your best bet is to jut get a new harness from a jdm place or junk yard it seems to be common issue for our cars

The harness or at least a wire or two has come apart. Is the whole left tail light not working when the drl's are on and braking? Thats a wire problem. If either braking light or driving light isn't on, it might be your bulb socket too.

Pull the bulb out and check the socket for any "green" meaning corrosion. If nothing is seen, check the plug for the taillight for any "green" as well. Sometimes the socket where the bulb goes into is pushed too far down and can't get a good contact between bulb and socket causing no brake lights. EG civic ones DO work but require one tab to be shaved down. Also, use some sort of dielectric grease (spark plug grease) on your harness connectors to ensure no further corrosion entering/ruining the connection.

Unusual but possible: do you have led bulbs anywhere in the lights? The huge resistance difference causes lights to malfunction sometimes. They were he'll for my lights