Car electrical systems are shockingly primitive. Window controls, for instance, are usually just eight circuits (two for each window). Close one circuit, the window goes up; close the other, it goes down.
Anyone with basic electrical skills could figure out how to make a set of controls for a system like that, and any gay man with basic carpentry skills could put those controls into an attractive, functional unit. (The remaining 99% of the population are screwed, though.)
There's actually an international standard that defines the form factor and interconnects for a car stereo head unit. Under WTO rules, it is probably illegal for car manufacturers to make highly incompatible units because it's an obvious trade barrier that serves no useful purpose, but factually the WTO is useless and corrupt even by the relaxed standards of an international organization.
