So my buddy has a 2004 silverado 2500 hd 4x4 6.0L, well recently there is a problem with the blinkers that also ties into the brake lights. well when you hit the left blinker it flashes but also the right brake light will flash along with the bed light. when he hits the brakes while the blinker is goin all the lights will light up includeing brake and blinkers. im hopeing this is a ground so if someone could direct me to the brake light ground and ground for the rear blinkers thatd be awesome, also has anyone ever heard anything like this before? any ideas on the issue? ill try to get a video in here as well as its hard to explain

 

anyone? we tried looking in his haynes manual but the schematics dont really help much and its almost impossible to chase the wiring on these things. already been pulled over twice because of it so we really need some help here i wana start with the brake light ground