Chevrolet Repair: 2004 Silverado 2500HD Trailer signals, ip instrument, fuse panel

Question
When signal is turned on both signals on trailer flashing. Disconnected trailer and tested pins in plug of truck and both pins are powered when signal is on. Tested at pins for fuses of left and right trailer lights at fuse panel in truck and they are both powered also with fuses removed. Can this be caused from the flasher unit or the body computer?

Answer
You may have a issue with the turn signal flasher located in the IP(instrument Panel) on the Drivers side.  It is located directly behind the D/S knee bolster, and plugs directly into the rear of the fuse box.  Also check the grounds under the truck located on the frame rail, above the rear differential on the drivers side.  May have come loose.
Jimmy