How can I troubleshoot/use a 14 wire motor encoder from Harmonic Drive?
Assuming that you are, in fact, looking at an encoder, it is an "absolute" encoder. Instead of ABZ, it finds all 12 bits of position in the encoder, then puts them out single-ended. Plus a V+ and ground. This isn't used much nowadays, since an ABZ interface is simpler and the computation needed to back out position is cheap, but it used to be fairly common, particularly in encoders with relatively high resolution. It has the obvious advantage that you get position on power-up, with no need for a home cycle. It has the disadvantage that the unit is more expensive : the encoder disk is more expensive, since it requires 12 tracks (one for each bit) rather than 3, plus it needs 12 optical sensors.

As for your specific unit, it is almost certainly no longer supported. I'd suggest actually phoning Harmonic Drive and throwing yourself on the mercy of a support person. Often, (especially if you find someone helpful) they'll go do some digging. Or not, depending on how overworked they are.