They are supposed to go at the end of a "tuned" race header. Old school you had to crawl under the car. Unbolt 3 bolts and drop the cap. Then you basically had straight exhaust through the header. These new electric gizmos make it so you hit a switch in the car and that happens. I guess you could put them anywhere along the exhaust system but the proper place is where the header bolts up to your exhaust pipe.
Pat