One output short

I want to control four indicator lamps on my front panel and I only have three outputs left on my mesa 7i77 IO card. I am considering using the extra enable outputs on the TB5 analog drive interface connector to run these lamps. I am using the old servo driver boards that were originally in my Tree Journeyman 325 mill and they do not appear to utilize an enable- or enable+ line. My plan is to use these 5 volt signals to trigger transistors which will control the12 Vdc power going to the indicator lamps. Does this sound reasonable or should I be using these enable lines somewhere on my serve controls and I missed a connection? I do have an enable line on the spindle speed controller, but that is actually powered via a relay that is turned on when the spindle is activated (that is the way the original logic on the 325 was put together and since it worked, I am leaving it alone).

The analog out enables are not useful for this since they cannot be controlled individually.

I would check you drives carefully for an enable signal, almost all servo drives have them.
It is a safety issue to be able to disable the drives on a fault like a following error
(sometimes the drive control is a disable signal = inhibit)

You can use a parallel port, the second 5I25 connector or a sserial expansion card connected to the 7I77 to get more outputs

Thanks for the info regarding the fact that the analog out enables cannot not be controlled individually. As far as an enable signal on my servo drivers, I have checked the drive servo schematics multiple times and have not found any such connection. Attached is a copy of the schematic for the X axis ACU. the schematic, as well as my physical verification of the wiring connections, only show seven wires being used. I am thinking that instead of an actual enable signal, the driver boards may be utilizing the Reset on pin 13 as a kind of enable function. Shorting pin 13 to pin 11, which resets the driver board, only occurs thru relay 1CR which is the main relay controlling the mill. If relay 1CR is de-energized it shorts pins 11 and 13.
Relay 1CR is interesting since it is energized through the a momentary (Reset / Enable) switch. It contains a self-locking circuit so once energized by a monetary switch, it locks itself on. The self-locking circuit goes through the estop, overtravel switches, the motor overload circuit, and one other relay which is label "Excess Error". If any one of these switches,circuits, or relays is opened, the self-locking circuit is broken and Relay 1CR de-energizes and shuts off the power contractor running the servo motors, disables the spindle drive, and disables the 24 Vdc power which runs the coolant pump , the mister, and the drawbar solenoid. As far as shutting the mill down if it gets a following error, this may occur through the Excess Error relay. It is energized if the quill exceeds its overtravel limits and it does have the possibility of being energized directly by the mills CPU. Since I do not have access to the mill's old software, I do not know what errors the CPU would trigger the Excess Error relay on. I would assume that a "following error" would be something that is detected by the main software and would supposedly then trigger an "Excess Error"? Until something failed on one of the processor boards, this mill has performed flawlessly so I figure the original circuit logic is pretty sound and I am trying to preserve as much of the original circuit logic as possible.
As far as my output issue goes, I was hoping to be able to do something clever to solve it. These indicator lamps are more of a "nice to have" feature, but they are not critical. I often refer back to the "distance to go" output to figure out what the mill is actually doing; "is it still plunging", "has it started the arc", etc. to enable a method of quickly assessing the current operation I wanted to use these indicator lamps to identify which axis is currently being driven. It would be nice if I could tie them into the "distance to go" information so they would lite if an axis is currently moving as well as if the axis is currently active, but I have stopped the current movement by zeroing the feed control.
Since I do have three outputs available, I can do only the x, y, and z axes, since those will be my main axes of motion, but if there is something clever I could do to get all three that would be great. I really do not want to use the parallel port since I will be plugging in a Sherline controller box into the parallel port to control my 4th axis which will be stepper motor driven, not servo. I do like Andy's suggestion about Charlieplexing. I was thinking that since I have three inputs available, that would give me the capability in binary terms to control up to seven on/off devices if there was some kind of IC I could input a three digital binary signal into (each of the three output representing a binary digital), and then set high one of four or more inputs. This Charlieplexing is along similar lines, but it is dependent upon being able to put the output signals into three distinctive states; ON, OFF, and INPUT(or a high impedance state). Does anyone know if three states are available on the Mesa 7i77 outputs. I got a feeling from reading, although I am not a electronics person by any means) that the outputs will only go high and low, which would preclude using the Charlieplexing approach, but it is a neat idea.

Are you using the 2nd port on the 5i25 for anything, or is that what you were going to connect your Sherline box to?