Do the knuckle test on the ECM case.

With the engine started and running... rap on the case with a couple knuckles or gently twist and flex the case with just your hands.

There used to be a lot of micro fractures in the circuit traces.

The other possibility is that someone may have removed the wire harness protective sheath that goes across the top of the radiator and several of your wires are rubbed through and shorting to ground