That's because your steering wheel is made of the same stuff. Cellulose Acetate Butyrate. it is a UV resistant and cheap plastic commonly used in the 60's to make plastic interior parts (and many other things) from. In Mopars, brown parts such as steering wheels, shifter balls, pistol grip shifter grips, etc. were made from it. Butyrate often has an acrid/sour odor, it's still a popular injection molding material except todays Butyrate blends have a masking agent added to hide the stink.