Well, one step forward, one step backward. Sigh.
My objective was to cross something off my list. The bad loom.
Before | After |
 |  |
The trunk wall wiring was first. The original loom was about 2.25" too short, so a new piece was made to replace it, and run all the way back to a harness junction by the air filter canister. Of course, additional work was needed on that end, and the wiring going into the MAT sensor did not please me, so I cleaned that up as well.
Yes, the retainer was clipped back around the loom, after this picture was taken.
So far, so good.