Identify the three wires from the XLR connector first:
1. Look at the bottom of the XLR connector carefully and you will find each pin of the connector are marked by a number, 1, 2, or 3.
2. Set your multimeter to measure resistance. Connect one pen of the multimeter to pin 1 of the XLR connector, and connect the other pen of the multimeter to each of the seven wires and get the reading for resistance. There will be only one wire showing a resistance close to zero. Mark or remember this is from pin 1.
3. Repeat the same procedure to determine the wires from pin 2 and 3 of the XLR connector.

Identify the four wires from the output transformer:
1. Connect one pen of the multimeter to any four wires that are left un-identified.
2. Connect the other pen of the multimeter to each of the three wires and get the reading for resistance.
3. If you get a reading for the resistance around 140 Ohms, these two wires are from the primary coil of the output transformer.
4. If you get a reading for the resistance around 45 Ohms, these two wires are from the secondary coil of the output transformer.