I believe on Lower Junction Box, the only place a tally power comes out is through the 8-pin LEMO for monitor, but you could have someone make a cable that runs out to an LED light that powers off 12v as well as provides power to the monitor (and tally too?).
On my PRO2 sled, I use the AUX line as a tally line and use an old Proformer box placed in the AUX battery position. It draws 12v power off the PTAP of the C/M or C position battery, sends 12v power up the AUX power line, out the AUX port through a cable I made to a photosensor that I place on the camera tally light (taped over, covered up, etc). If light hits the sensor, 12v power is passed thru the photosensor, down the AUX GROUND line and back onto the GROUND pin back into the Proformer box. I then have two RCA style plugs that I can connect, one to the monitor tally input (the Cinetronic Gen 2 had a separate tally in, my SmallHD DP7 doesn't), the other to an LED I place on my monitor to see tally.
I think if you look up Peter Abraham's old wiring diagram for the tally system based on the 9v battery and photosensor, you get an idea of how tally lights can work. Then just get creative. In most situations, if you need a tally line, then you also likely have a dead line somewhere on your sled to use as tally.