OK. Wiring Harness has been repaired now. I cut out the crusty looking corroded splices and re-crimped them using an open barrel splice. This was then sealed in with some adhesive lined heat shrink. I wrapped the loom using a mixture of non-adhesive vinyl tape, and fabric type loom wrap.
Here is the end result. I found it difficult when putting the loom back together to find a decent reference picture for how the loom should look, which wires branch off where etc, so this picture can be added somewhere for reference material.
The white tape marks the places where the splices are located within the loom. Note that I didn't remove the original loom binding in the section leading up to the fuse box connections. There could be further splices here, but i decided i'd leave them alone. Other than that section, I've had the entire loom apart.
The most corroded splices (and the one that was completely broken) were found in the section with the two white bands to the left of the manifold loom tunnel. This is where the majority of the splices are found ( i think i re-did 5-6 splices in this area)
This is the area of loom that drops down below the coolant connectors to the throttle body, and the loom forms a low-point when installed. My thinking is that this is the area where the water collects off the rest of the loom and drips from, and can become saturated with water. This penetrates the 25 year old splices and corrodes the connectors. Toyota use a sheet of what looks like adhesive lined tape folded in half, to cover their splices. All the ones i had removed, the adhesive was crusty and dry. Definitely age related deterioration. With new, tighter fitting adhesive heat shrink installed, i'm hoping this repair will now be good for another 25 years.
Here is everything buttoned back up again after installation. As a side note, I finished the job with no bolts left over. The car also started first time with no connectors forgotten to be plugged in. Alternator is now charging a strong 14+ volts when running. First engine related job of this nature I've done so it's been a learning curve, but pleased with how the results came out nonetheless.
but now added to Know Your 2