I have exactly the same problem. I tried to solve it by buying the 7D Dummy, cutting the end of the cable of it, cut off the 7,5V 2 pin XLR cable that has been provided with our package of PRO AIM RIG-2100, and let my dad solder it together nicely. Afterwards he ducktaped the 2 ends so it looked more aesthetic. Still my 12V monitor does work with the 3 pin xlr, but my 7D doesn’t.. Why? Anyone ideas?