Count the wires.
A four lead set has four wires.
A twelve lead set has 12 wires.
It doesn't matter.
Disconnect one lead set from the neutral stud. Both leads together if it is a 12 lead set.
Connect the disconnected leads to one of the other line leads.
Use a continuity tester to avoid connecting the winding back on itself.
Tape the connection and forget it.
Now you have two line leads and a neutral.
Of the original three line leads, one will remain, one will be taped up and the other end of the winding('s) that you disconnected from the neutral stud will be the second line lead.
You will have a single phase, in phase output.
The KW capacity will be will be 2/3 of the original KVA capacity.
The KVA capacity will be will be 2/3 of the original KVA capacity.
The PF will be 100%, 1.0, or unity.
This is the preferred method of reconnecting older sets.
You need only one simple check with a continuity tester.
You don't need to see wire numbers that may have become lost or illegible.
Your 187 KVA set will become a 125 KVA, 125 KW set.
10 lead sets may also be reconnected but it takes a little more work.
A bar-diamond or Collin connection is used for 10 lead sets.
Voltage regulator connections? Connect line to line and adjust the voltage for a 208 Volt regulator.
If you must have 208 Volts for the regulator, connect to the taped up joint and to the other line lead.
If I have to explain how to connect a 120 Volt regulator, it would be better if you hired professional help. (For the whole job!)
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Ohm's law
Not just a good idea;
It's the LAW!