THis is a good example of a cheap design that costs about 50 cents to make in CHina. What did you pay?
REMOVE all 100 Ohm resistors for 27 V use. I assume you didn't get instructions.
THe middle Resistor is beyond rated power with taillight on only 380mW so will rather hot to touch and should use two 1K resistors or so in parallel for cooler operation.
Tail light total LED current is 26 mA divided equally in 4 serial strings or 6.5mA ea.
Brake light total LED current is 126mA " " " " or 31.6mA per LED , which is beyond rated current but OK for short durations . It will run the junctions up to 100'C in a few seconds, but for an hour a day stopped in rush hour traffic, it will work but not as long or as bright if using 50mA Ultrabright LED's with 4 leads.
But to make the design work as intended remove all 100 Ohm R's for 24~28V operation and leave in for 12~14V operation.
Red is brake +V switched and greenish is Tail light +V, while black is chassis ground. ( American convention)
The central located tail light resistor will be burning hot and dissipates 420mW driving all LEDs and looks to be either 1/8 or 1/4 W RATING. ( CHange with two 1K resistors might be better. It may work and will not live it's full life of 50+ yrs but might last as long as life of LEDs ( possibly 5~10yrs). ( who knows with this cheap quality how reliable these LEDs are)
LED Vf may go from 2.0 to 2.2V with brake switch ON
supplier tolerance unknown, they could be much higher.. i.e. 2.6V meaning cheaper quality.... but then cooler central R.....
Simulation tester