In my car i use 2 of these COB leds, the adapters are included. https://nl.aliexpress.com/item/4000283053353.html?spm=a2g0o.productlist.0.0.47997b0a19ZqAB&algo_pvid=afab7b0f-9879-4609-b63d-8d0ec96fd298&algo_expid=afab7b0f-9879-4609-b63d-8d0ec96fd298-0&btsid=0ab6f81615957714210671566e48d4&ws_ab_test=searchweb0_0,searchweb201602*,searchweb201603*
The problem is that the COB leds are working perfect on 12,0V DC, i tested them before installing with a DC power supply.
I do not remember the exact current at 12V, but they are bright at 12V and do not overheat.
But the voltage in a car can be 14,4V and that is too much for these COB lights, they get very hot in a few minutes and will not last very long.
I installed them with a 15 Ohm 2W resistor in series, with that resisor they will not overheat, and they are still much brighter than the original 5W lightbulbs.
Most of the festoon replacement led “bulbs” are just 4 leds in series, without any current limiting, they will work, and they are very bright, but they do not last very long because they are made for 12V instead of 14,4V.