Do I need a new ECU?

So the wire to the front O2 sensor on my 1996 got into contact with the header, melted, and blew the "METER" fuse. I replaced the O2 sensor and replaced the fuse, but now get a CEL for p0135 - O2 Sensor Heater Circuit Malfunction.

I have 2 good O2 sensors - heater circuit resistance is 16ohms cold, and "bench testing" with a propane torch shows roughly the right voltage swings.

I have checked the harness with the sensor and the ECU both unplugged. The heater circuit 12v+ does go hot with the key on. All wires in the front O2 sensor harness are not shorted to one another, and not connected to ground.

With the ECU plugged in, however, the sensor heater circuit ground actually shows 300-400 ohms to ground, key on or off. That seems like a problem, no?

Any ideas for troubleshooting further? Anyone have an OBDII NA ECU sitting on a shelf I could plug in for a quick check?

I have the factory ECU from my 96 in the garage if u want to try that.

Pm sent