Ok, I had to re-write this. I thought you were dealing with the armature cables as there is little current in the feedback cable to burn it out.
The control is not getting the feedback from the pulsecoder/encoder/resolver/ whatever you have connected as feedback.
Swap the feedback cables at both ends. It will never run just switching the cables at the feedback module. This should tell you if it's the cable as the Y axis won't "run away" when powered on(unless the cable is bad). If cable is bad then the Y will run away and the X will not lunge with y's cable.
If symptoms are the same(x still running away) then you will need to power up the feedback device with 5V and connect a scope to the signals:
G1-S2
G2-S4
S1-S3 marker
R1-R2 5V
above is pulse coder.
Rotate the motor shaft with power connected and observe the signals above. Make sure you have 5V at R1-R2 with machine on. Check with cable disconnected and connected.
Jack of all, master of none
Galveston, TX