Electrical continuity detection [Manufacturing Solution]
A classic, if complex solution to this, is to superimpose a defined signal on the source test lead.  It can be a simple low level square wave, or a digital pattern.  Say somewhere around 20kHz to 40kHz.
On the other other wire in your continuity tester, you look for the transmitted signal, and only energize the test voltage if it is present.  You can do this with a 555 timer chip and a PLL like a 4046.
Just make sure that the supervisory circuit is protected from the high voltage.