Q: Mixing incandescent bulbs with LED's in a car

Generally speaking, mixing incandescent lights with led’s should not be a problem. However, it has been my experience that there are a some vehicles that will use a lighting control module to control accessory lighting, and led’s have much less resistance than a standard bulb. In some of these vehicles, the lack of resistance can cause a fault code, or light, to set, because the lack of resistance makes it look to the module like a bulb has failed. I would suggest replacing a couple of bulbs at a time and see if it causes any warnings. Mechanically, it should not cause any issues though.