can you get at the wire colors?
red is OFTEN power
black is OFTEN ground.
Get a logic probe after you make your best guess for power and ground, look for pulses on the other lines.
How may wires? if four you're looking for +, -, A, B
if five you're looking for +, -, A, B, Z
if seven you're looking for +, -, A, A-, B, B-, Z
if eight you're looking for +, -, A, A-, B, B-, Z, Z
A is channel A pulse
B is cannel pulse
Z is index pulse
- is for differential