I need help with 1988 Chevy C2500 OBD1 System. ECM is heating up and failing.

The ECM container box heats up and that is when it fails to communicate....no data and will not give code 12 or any other codes. I cool the box down with a high speed fan and I get my ECM back,,,,it works.

Does anyone understand what is going on here?? Is it a sensor with a problem causeing this or is it just a bad ECM?. I guess it could also be a short somewhere but I can't find one. I have the wireing diagrams and have traced and checked twice.