It will die after 1-6 month!
The most tenacious what I find was this
But after some month some of the lines of leds will die. But it will work with leftover LEDs.
Why? Because of hot. I mean it is not with aluminum pcb, it is with glass textolite what can not let heat away from the leds. And it is with ordinary smd resistors. When car is muffle - it is about 12v, when engine is work - it is about 14v. Current with 12 and 14v is different.
Also there is really cheap leds with tiny crystal and they work to the limit (works with maximum current)
I upgraded C5W by aluminium radiator 14x14x6mm, but it is also with glass textolite with poor thermal conductivity.
Now I finalized drawing the pcbs for C5W (C10W) and finally (15-20 hours) pcbs for W5W (T10) LED lamps with TRI-R 3030 smd LEDs SunLike and NSi CCR - Constant Current Regulator & LED Driver (I call it smart resistor)
How much time need to draw pcb board?
If someone interesting, C5W will cost about 5$
W5W (T10) will cost 5-10$ (depends from led quantity)
1pcs 3030 SunLike led cost 0.5$ in my web-site
I’ve been trying to find good T10 and 31mm festoon globes for SO long. Infuriating that either nobody makes ~5000K in them, or they say they do but they’re 6500K when they arrive.
A long time back, like 4 or 5 years, the best answer I found was a spring-loaded festoon adapter that ran a power lead to a square pcb loaded with LEDs. The product was aimed at RV lighting and had two other adapters included as well. Mine was roughly 4000K, though I have no doubt it is low CRI. But that may be another strategy to look into, using the adapters.
(I tested and a Google search for “festoon adapter LED” shows examples. )