Q: Ok here goes, I have a 2001 Firebird, a year or so ago my son changed out my original factory stereo with a JVC stereo and when he

Ok here goes, I have a 2001 Firebird, a year or so ago my son changed out my original factory stereo with a JVC stereo and when he did all of my instruments quit working (speedometer, gas gauge, oil gauge, etc) so he “re-wired ” & was able to get the speedometer, mileage and the temp gauge to work but the oil, gas & battery gauges just flop back and forth all the time. Recently while driving sometimes my car will just shut off, but then it will start right back up when turning the key, the last month it is shutting off more often so I took it to a stereo installation place and had a new stereo, electric start and alarm system put on it, it no longer shuts down but now NONE of my gauges work, now when I took the car in they said “brain wasn’t in the car” & I would have to purchase a new one for $200 which I did and since none of the gauges are working still they told me that the “module” is out on my car, so are the brain and the module 2 different things? so now I am confused

My car has 18900 miles.
My car has an automatic transmission.