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I have the same 1997 5.7L V8 GMC W4. The issue I am faced with is that O2 sensor J110 and J111 in the attached diagram will blow fuse F16 when power is applied together. Power line black and red had melted in some areas and I had to replace part of the line. Even if I try to split the power line, it will blow the fuse. If I run 1 red and black line to 1 of the O2 sensors, it works. The readings I got from back probing J110.
The damged wires you repaired may be effect rather the cause, my first move would be to remove the fuse and disconnect all four sensors.
(1) Simple resistance ohms test between red-brown wire and ground.
the fuse out and everything disconnected you should see very high resistance.
If the resistance is low then you have a short in the actual wiring.
There are techniques to locate the position of shorts in wires but for the non-tech eyes and touch wiggling the wires are the way to go if that dosn't help it is really case of actually making a cut or cuts in the wire to locate which section the short is in.
If the resitance high indicating the wiring insultion is intact you may have a short internal to one of the sensors.
(2) Resistance check on eacthe h individual sensor heater.
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