Seeking Wire Wisdom

[60ShortStepGMC]

Background
The after market turn signal assembly (sig-flare 900) kinda worked, just not exactly right. I yanked it. And, in hopeful new-guy style, I refurbished my steering column turn signal assembly and switch. When I plugged the harness to the stock switch... nothing (not really a surprise I suppose). No turn signals front or rear.

Now, after making these changes, when headlight switch is pulled full out I have no rear lights and when headlight switch is pulled half out my turn signal controller ticks while heater fan whirrs in unison.

Assessment
Looking at everything under the dash, it seems a newer-ish wiring harness section was added. Everything else fore and aft of this area is old. Also, there's only two wires from fusebox to dash: cigarette lighter, which I added, and heater fan.

It seems to me that I have two options: 1) reinstall the sig-flare assembly and limp by while saving money, or 2) work through the harness one wire at a time, spending money here and there as I cut/splice as needed to match the specs.

I'm leaning strongly towards option 2. Sure, I may use all the same colored wire but I'd label it all, solder it all and learn much about the schematic. Anything I do would surely be an improvement. But, I'm susceptible to new-guy hopefulness. Which leads me to my question(s)....

Sanity Check
For those of you older, wiser and more experienced than I, do you have any insights? What are the obvious pitfalls I may encounter along the way (either option)? What other things should I consider?