need help on wiring harness question 94 e320

[fulltimefamily]

Thanks for taking a look at this.
I suspect that these wires (shown in photos attached) are not part of the wiring harness being replaced in the DIY article.

I hope this shows the location in the three photos attached.

This assembly seems to have one white/purple and two smaller brown wires. The insulations is badly deteriorated on all three.
They proceed from the firewall joining with a heavier wire (which also comes out of the firewall in the same location) into a protective sleeve near the oil filter housing and continue down where the heavy wire attaches to the starter solenoid. I can't see where these three damaged wires branch back out and attach.

By the way, I took it to my mechanic because my mileage had dropped from 25mpg to 19mpg and my check engine light was lit for two weeks before going out on its own.

He checked my codes
Resulting in: 42-injection valve cylinder 2 short to battery voltage.

No codes or check engine light after resets and test driving
No lean or rich fuel indications by test equipment.

My Question is: What wires am I looking at and can a DIYer replace them?
Could they be the culprit in poor gas mileage?

Although, I realize that the main harness is probably bad too, I wondered if these wires should be replaced first and perhaps cure my current woes.

Any thoughts welcome and thanks for all the information I've gleaned by lurking and reading over the past few months.Attachment 31750Attachment 31751Attachment 31752