I threaded a cable in from outside, got it connected, and prepared for my victory dance.
However, when I operated the slide, there was all kinds of noise that meant trouble.
After much time, effort and investigation, including the dreaded removal of the fascia
I discovered the cable had NOT threaded onto the pulley when I poked it in from the outside, but instead it threaded between the pulley housing and the plastic jamb. Without realizing that was the case, I had threaded it through the 2nd pulley and got it connected. Well, it got chewed up, of course, when I operated the slide. And other bad things happened, but I finally got the damaged cable removed.
Fortunately I had purchased an extra replacement kit to have on hand. But I still had to thread that cable through and successfully hit the pulley. This time, two things helped. 1) I had someone inside watching where the cable was going; 2) To help that person see better, I had a flashlight shining on the appropriate area inside the trailer. Well, the flashlight actually allowed me to see through the hole from the outside so that I could see the pulley and tang, and get the cable where it needed to go. That was a stroke of luck, because I'm sure my helper would not have been able to see the tang.
Now, I think I have a tension adjustment problem which I'd like to resolve. The motor or gear box makes an unusual noise at a certain point. But I'm not sure of the proper tension settings, so I'll have to study up on that. I'm not quite ready to give up and take it to the dealer just yet, but it may come to that.