I have a 1991 GMC 3/4 ton 4wd which shows the brake light trouble symbol on the dash "I' "p". I replaced the front brake pads and the rear brake shoes are at least 1/4 inch thick still. I ran a diagnostic and it shows no codes. I disconnected the battery neg terminal for 15 minutes. no change, then I disconnected both wire connection assemblies for 15 min and after that the warning lite was still on. what do I need to do to make sure my brakes work and to get this warning lite to go back to normal.