Some more updates for anyone following still
Seems the mystery plug does and does not have anything to do with the no start issue.
It seems to simply be an access plug, can do more than one thing.
I have no books, no real schematics. so am flying blind and learning as I go.
Making calls, asking on FB. Going whereever I can to try to find information.
Ironically one mechanic actually suggested going here to Skoolie and looking for someone called Chris cadillac something.
On the Vista what I didn't realize is the shifter is "upside down". I admit that when I was worrying about wiring and what not I never paid much attention to the linkage itself vs the position of the transmissions selector.
When I swapped the transmissions the mount and throw of the cable is different.
So on the vista I was worrying about the plug, and in reality the whole time I was in 1, 2, or 4 on the selector when I thought I was in R-N-D.
No worries, I'll make a new label. I tried to spin it around, and if it wasn't for the vista dash style I could simply reverse it and it would be normal. But it is ok, different is good. and it works fine, all gears, no binding.. just "upside down"
I was playing around with bus 89 and even bypassing the neutral safety switch no start. But I decided to try same on vista and it started..
It was then that while moving the gearshift through all ranges I was surprised that all the way down was now reverse.
So the vista is pretty much done. I do need to figure out how to hook up the Economy mode switch but now have a good idea of how I think.
Bus 89 I am unsure why it won't start... is def some kinda safety interlock or something I missed, so that is today's goal. Once it starts I think it will be fine. It now has the 98's computer in it... and the Vista has the 03 Computer... Vista popped no codes on startup and it idles fine, a little lower actually than with the 98 ECM... just a hair.
I'll update again when I get bus 89 moving. Once I can get it out of the way I can take the vista for a spin and see what happens. Other than programming possibly I think it will be just fine.
For anyone needing it in the future I did find out this about IH cuircuits.
Circuit 94 - Antilock Brakes
Circuit 92- Electronic transmission
Circuit 62 - Instrumentation/warning light
Circuit 13 - Ignition 12V pos
Circuit 12 - ACC 12v
Circuit 24 - Ignition
If that ever helps anyone down the line