I don't know if there is a professional linguistic explanation for that --I haven't found it, but the use of what verb form is used in these cases corresponds to what they were related to from the start.
Your examples point out rightly that these nouns are related to an activity, but I think the case of "pastilla de encendido" is different, because the idea of "encendido" (similar to Alec's examples) already existed before those "pastillas" were sold, so I guess that is why their name is associated to the past participle instead of the action of turning the car on. They could have been called "pastillas de encender" or "pastillas encendedoras", but I think they wouldn't have been immediately associated with the parts of a car involved in the process of "encendido".