Ethan,
The first thing to do is work out the individual windings using a DMM set to the "Ohms" range. Take each wire in turn and test for continuity between the other wires. When you find continuity, write down the connections (or tape the wires together if flying leads). If you find three wires all showing continuity, then you have a CT or "centre tap" winding. The centre wire will be the wire that is disconnected when the other two wires show a maximum resistance reading.
If you find 4 or more wires showing continuity, it's probably a multi-tap mains input primary.
Once you've done this, you can see how many windings you've got, and what connections are which. Next, you need to find the voltage ratios. I find the easiest way to do this is using a small 6V transformer (the type used in cheap cassette recorders or portable radios). The theory here is that 6V is a low-enough voltage to not cause any damage to the windings.
Connect your 6V ac from the small transformer to a winding of your unknown transformer. Then carefully measure the ac voltages at the other windings. Switch off the power before changing the meter probes- say for example the winding you've connected the 6V to is actually a 6V winding, and then you touch another winding which is rated at 240V, then 240V will appear at that windings terminals!
You'll now have a voltage reading next to each winding. From this you can work out which winding is which. The mains winding is usually instantly recognisable- especially if it's a non-tube type transformer. With a lower-voltage type transformer, you'll see a massive ratio between one winding and all the others- this is the mains primary.
I hope this helps- I've managed to salvage many surplus "unknown" transformers using this method. Let me know when you've worked out which windings are which, and we'll see if we can work out the rest of the ratings.
Of course, the easiest method is if someone has a data sheet already for this model :wink:
Mark