How to test the ECM and Wiring

Does anyone know how to check the ECM and wiring?

For what?

Sure, you basically check all power and grounds to the ECM.....as far as inputs and outputs go, you check those that are causing problems that you are looking for.....ability to read schematics, schematics, and a GM scan tool would be necessary.....

You don't tell us what year the 98 is, or what your "concern" is.....