This is a "cat eyes" tail light and has 2 separate lights (see Ebay link)
There are 4 circuits and 3 types of components (LED, resistor, diode):
1.Yellow wire (turn signal, 8 LEDs)
2.Red wire (brake, 6 LEDs)
3.White wire (tag, 3 LEDs)
4.white wire (run, brake LEDs, half bright)
Circuits work as follow:
1. and 2. Yellow and red are identical: one resistor and 2 chains of LEDs
White "tag" circuit has resistor, 3 LEDs and a diode, which has no purpose(?) and can be removed (Chinese electronic guy was probably drunk, engineering the tail light)
White "run" circuit uses same 6 "brake LEDs" half power because it has 2 resistors (why 2?), it also has a diode, which is not needed (?) and can be removed.
Diagnosing and repairing of $15 tail light is more like entertainment.
So far I found 2 bad resistors and 2 bad LEDs. A few resistors work but look burnt.
After my "high level" diagnosing 3 more LEDs stopped working.
Improved diagram: