need help service 4 wheel light

From : john rc

Q: i have 2001 dodge dakota 4.7 auto trans 2 wheel drive. service 4 wheel light came on and will not go out. i have been told by dealer it is in radio or it is in the heater/ac controls help. also is there a way to put dual exhaust on truck not cat back but total duals ps. 225000 miles plus mileage is still above 20mpg. however the trans is in dire need of rebuild now. changed plugs at 200000 was still running strong with old ones. also have 245/75/16 lt 10 ply tires on truck mileage is off by 3. it is showing 30 when it should show 35. checked with radar .