Lloyd,
Congratulations on your purchase. The sustain pedal from Yamaha won't work on KETRON products as the polarity is reversed. You'll either have to get a Sustain pedal with a polarity switch or a KETRON sustain pedal. All manufacturers use different polarities for their sustain pedals. If you do have a pedal with a polarity switch, turn off the SD7, switch the polarity - then turn the SD7 back on.
The SD7 has polarity switching for volume pedals but not sustain pedals :-(
Thanks,