ST-Link V2 Programming STG-850 PLC -- STM32
The problem here was bad wiring. The root cause was a misunderstanding of how to identify the cable connector pinout. 

I was basing my pin numbering solely on the center rectangular polarization notch. The result was that when I viewed the ribbon cable connector from the bottom I had it mirrored and was connecting GND to where I thought SWDIO and SWCLK were. The VCC pin did coincidentally mirror which allowed the power status indicator to come on. 

A friend pointed out my error by noticing the small (faintly) raised arrow on the plastic cable connector indicating pin 1. 

So, in the end it was a novice error of not distinguishing between a top-down and bottom-up view. 

Once it was wired properly the ST-Link connected fine.

Thanks for the help everyone.