I recently swapped the transmission in my 95 850 turbo. with a recently rebuilt one with 40k miles. The gears change smoothly but that yellow light came on and stayed on. Any ideas as to the cause?

 

Normally it means that you have overdrive locked out. Maybe it could mean other things too, but that's the normal meaning. You push the button and that light comes on. Push it again and it goes out. So hopefully it's only that.