Ok. I was looking at the moog guitar, and I thought, why couldn't I just get a keyboard sustain pedal, and put another jack in as an output so it goes from guitar to sustain to amp? Presumably this would create the same effect as it has on the keyboard. Am I completely wrong, or would it just need more than the one new jack?

"I don't have an instrument, I don't have a great voice, I just have some nice clothes maybe." paul rutherford
I assume that you mean you want to plug your guitar into the keyboard sustain pedal and then into an amp to give you infinite sustain or something. Well I'm afraid it doesn't work like that, keyboard sustain pedals are only a foot switch, they have one output jack and no input, it just goes into the keyboard to tell it to sustain the note, the keyboard does the sustain not the pedal.
I'm not sure what you're expecting to do...

If you're hoping slapping a jack in the amp, and plugging the pedal into that will create a sustain effect, thats not how it works.

A sustain pedal is pretty much just a switch in an enclosure. All it does is connect or disonnect the sleeve and tip of the jack, so theres no internal effect in it..