I would never use that Y cable hack because the sustain, rotor and expression pedals all output a voltage (for the Nords this is 3.0v) that is tested to detect the pedal status.BluesForJonny wrote: So, I used a simple 1/4" Y-cable (splitter): (1) 1/4" F x (2) 1/4" F. I cabled the 1/4" M from the FC5 into the Y cable, and then (1) 1/4" M - 1/4" M patch to the YC88 Assignable and (1) 1/4" M - 1/4" M patch into the E6 rotor pedal port. Low-tech for sure, but works like a champ and cost under $10 and it works for both machines whether they are MIDI'd together or not. (see my post for the MIDI on/off footswitch, if you are interested).
If you use a Y cable, then you are connecting two voltages coming from different instruments and that is certainly not what the respective circuits expect. In addition some instruments expect "normally closed" and others are "normally open" switches and voltages (and potentially polarity) as well as detection circuits are likely to differ.
This might have worked for you in this occasion but equally you could fry one or both keyboards just to save buying another cheap pedal.
There is a good reason why there are special pedals with two internal switches (and two cables) to do exactly what you want to achieve.
Alternatively I would velcro two pedals together so I can step in one, the other or both and be sure that it will not damage anything.