HI, I have used 8 Ohm / 25 watt resistors parallel to the LEDs in my daughters car. Its no Volvo, but you need to simulate the current used by the bulb. An indicator bulb of 21W uses +/- 1.75A at 12V. (system is more like 14V so 1.5A). 14V / 1.5A = 9.33 Ohm. 8 Ohm/25 Watt i had laying around here so...