The ECM's from 1997 and 1999 are not compatible.

It sounds like you have an open cable between Pin 52 of the ECM (coil cylinder 2/3 output) and the coil itself. Yes, the yellow/white wire to the coil for cylinders 2/3 should pulse while the engine is running. If it reads full battery voltage with no pulse it's open, or it's possible that the ECM driver output is bad.

Check the connector to the coil carefully. Yes, those cables can get brittle over time. If that's good do a continuity check back to pin 52 of the ECM. The ECM is located under the passenger side carpet.

If you have good continuity it sounds like the ECM bit the big one.