Wide black tape. Exactly how I handled it, but using the original harness. Some wires were not biodegradeable, while others were obviously disintegrating. With the whole of it streched out on the picnic table, it was easy to replace just those wires that needed replacing. I didn't foresee any plug-n-play engine swaps in the future of the 84, so I did away with that gray connector on the firewall.

You can get the original vinyl sheathing brand new from, for example, http://www.waytekwire.com, but that Scotch 33 is holding up spectacularly 50K and several years later. Don't skimp on the tape quality or you'll have a gooey mess in short order.

By the way, on that compression check suggestion: I thought I'd read that you changed all injectors but still found one seems to be weak or dead. Now you've proved to yourself all are wired together, you could swap it around to another cylinder, or make certain that dead one is alive somewhat by grounding its plug wire for a couple seconds.

It is reasonable to look for the cause in all that recent work, but remember you're much more focused on the symptoms now than when you started. At some point, put a meter on the oxygen sensor to see what it thinks of overall mixture. You can also see its transitions using a meter at the pink test point wire, but don't expect to light an LED with it.