From what I can gather, America on Parade ran two times a day with an afternoon show and a later one immediately before the fireworks. I would think that they had some lighting on the floats for the later show.
Disney ran a special on the parade and here's the segment showing the whole parade, at night. The lighting is nothing like the MSEP:
http://www.youtube.com/watch?v=aTw0sDdLDTUMore digging found this next video, which is a slideshow from the WDW MSEP:
Dailymotion - MAIN STREET ELECTRICAL PARADE (Walt Disney World)
I just fast forwarded to each picture since it lingers too long on them individually, but at about 5:00, you can see the Pinocchio underwater portion with the Monstro float in the rear. I think they used some of the same photos that Jeff has to fill in the gaps but the cars and Monstro float do fit in though. There's also some shots of the neon finale in there.
This guy has some other interesting videos/slideshows.
This is supposedly a video from opening night. Some of the floats are hard to make out thanks to the video editing and low quality but is still really neat:
Dailymotion - MAIN STREET ELECTRICAL PARADE (June 17, 1972)
Enjoy.

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