I decided to make a tally system that works internally on my PRO HD sled, since I'm not crazy about running cables outside of my rig... pretty much ever. Here's my concoction:
Typical photosensor tally, but I stuck it in a coily cable with the 2-pin LEMO for the AUX line.
The guts of the tally live inside a hollowed out Proformer battery. Draws power off a PTAP running out the back of the unit and onto the camera/monitor battery. I have it working with the 2 battery configuration, but should work with 3 battery configuration, so long as a camera battery is there (and for balance, I'd imagine it always will be there). The RCA plug on the right goes to the tally input on my Gen 2 Cinetronic, and it's regulated to 5v with dropoff below 2.5v, so the monitor detects the tally properly. Left RCA plug is for standard LED on a cable.
A view of the total bottom section.
Cinetronic Gen 2 triggered tally, everything lit and working.
I still need to make a few spare cables as well, but only finishing touchesis hot glue and closing up the Proformer down below.