Question about Airpax servos

After some fruitless web-searching, I have a question for the group.

Since I'm not very familiar with servos, I'm trying to figure out one of
my latest finds: an Airpax servo.

It's marked as using 30VDC. It has an encoder (of cource), and while I
haven't tried to count the itty-bitty teensy notches on the encoder
foil, the foil wheel has a convenient number marked: 432

I would have assumed it to be a brush DC servo, except for two things:
First, there is no perceptible 'cogging' by turning the shaft by hand;
it spins quite freely. Second, There are 3 wires, not two, going into
the motor body.

Wiring for the encoder is going to be fun...there are ten wires in a
ribbon cable coming off the PCB on the encoder end. Which is all the
more puzzling...there are only 5 leads to the optical head.

Can anyone shed a litle more light on what I might have here? I haven't
encountered a DC motor that uses 3 wires before, what's up with that?

Any info will be appreciated, prior to my applying current to motor and
'letting the smoke out'.