Leith,
Ok I looked real quick and instead of an Indexer, it may have been external coolant. The TB3-21 is what I thought would have been 22 for the index trigger. 21 is where flood coolant, and spindle fan hook at. I believe 21 only becomes live when the spindle is "on".
This is what I have for the numbers.
TB3-1 (+24V Positive 24 volts at all times - comes from TB4 power supply)
TB3-16 (Negative - also connected together with TB3-15 and 17... they all tie to the ground stud in the controller)
TB3-21 (+24V Positive only when spindle is on = I will check this on my machine to see if it does only fire when on)
TB3-23 (I don't have this one listed in my notes, but will find out. From the previous indexer schematic it shows as positive)
I think it will be for flood coolant. If the machine did not come with it, then I could see Lockheed adding it as they would use coolant. Just odd that it is 4 wires, as I would think they would only need 2 as a trigger. It all matches up for the indexer, except for 22 is the indexer not 21. But 21 does have the flood coolant tied to it. Will do some more research tomorrow. I have to get in bed, already past midnight... time flies, LOL.
Will be back tomorrow,
Robert