On how to keep the wires attached to the connector for the MS. Car started acting weird and spiking rich on Sunday when I was over 100 miles from home. Turns out one of the ground wires in the standalone harness broke off the connector...again. Any tips on getting it to stay there for good?

 

I soldered mine proper with heat shrink. *knocks on wood* almost a full year now without issue of a wire coming loose..

 

Where exactly is the break occurring?

Having not seen the connections, is it possible that you're forming "cold" solder joints? If you don't put enough heat into the joint to get both the wire and the pin up to the point where the solder flows freely across them, you will wind up with a connection that is prone to fracture at the junction between the wire and the pin. Cheap irons will tend to cool down when you're working on a heavy wire and can produce this phenomenon as well.

Having said that, I've built 3 or 4 of these now for people, and I've not heard of one failing yet. I do use heatshrink over each individual wire, and I've been doing this for ~20 years so I've had a bit of practice.

 

The break is occurring right where it's soldered together. I'm going to take a soldering iron home tonight, pull the harness out, and re-solder pretty much every wire so I don't have this issue again. (or the new owner...)