The static strap is required at all times to prevent spikes. It should be under the left side, touching the ground. It is not like a chain dragging, but is a wire connected to a 10 thousand ohm resister.
you may have a crack in the system card or power card. A coiled resister on the board often beaks its connection. I'm not sure if you have any schematics or manuals for this. You should check for shorts to frame. Unplug the battery and use an ohmeter from the neg and positive to frame. There should be more than 10 thousand ohms. If not, you must find the source of the short by unhooking components. If no shorts are present, have the truck jacked up and running in drive. grab the harnesses and wiggle them lightly, also touch the system card and power card and see if the code appears.