Help fooling vehicle diagnostics
it depends how tight the tolerance for bulb power rating is assumed in the car lamp fail detect circuit. 

However tungsten lamps are 10x lower R when cold so the current surges then decays to 10% when hot.

14V 5W  R=V²/W=14²/5 ~ 40 Ω hot and 4 Ω cold times 2 in series = 8 Ω which would draw 50 watts with 14V with a fixed resistor when LEDs are turned on.

The threshold depends on the duration of the pulse.  I would start with a 1000uF capacitor and a 1k 1/2W shunt resistor and see if that reduces the flashing and warning.