I have a Yamaha P85 (as of yesterday), and two individual foot pedals with 1/4" plugs. The DP has only one female plug for sustain, but also has a female plug for "pedal unit," which combines the standard pedals into a plug that resembles a PS/2 plug for a computer keyboard or mouse.
Any idea where I can find which pin means what in this female PS/2 connector? I would guess this PS/2 plug is standard for DP pedal units, and I bet it would be possible to wire up my two pedals into this plug with room for one more later on.

The only standard is the 1/4" jack. A 1/4" pedal is just a simple contact switch.

The "PS2" plug might be a common to Yamaha three pedal units but is certainly not an industry standard.

The only other standard for pedals is MIDI but you don't see this used much

But I bet someone who has a three pedal unit and an ohm meter could figure this out for you.

I actually built an pedal adaptor once so I could use a new M-Audio pedal with this old 1980's keyboard that took an oddball special pedal that you could no longer buy. It really helps if you have a pedal you can analyze.

I was looking into tracking down information on midi pedal design for use with my keyboard when I came across the following site:

http://diykeyboard.org/yamaha-triple-pedal-connector

Now if I could only find a diagram for the Privia - and the connector they use.

Rich