If you look at this post, it shows to connect the 7747 park neutral wire to E5 when converting to the 7427. There's another post that goes into more detail, but it didn't come up in my quick search.
http://www.gearhead-efi.com/Fuel-Inj...7+park+neutral
There 3 range signals from the transmission going to the 7427, different combinations of these 3 tell the ECM what gear the trans is in. Grounding only E5 tells it that it's in neutral. I don't think there's a wiring diagram that will tell you that, though.