Hello and welcome.
I assume you mean a MacBook Pro (Retina, 13-inch, Early 2015)? The 15" model is a Mid 2015. Either way, that is a very involved repair as you found out, and not a user-serviceable part. It is not recommended that folks attempt this type of involved repair, as it is very easy to damage internal components when performing that repair, without proper training.
That said, it sounds like either the keyboard cable connector isn't seated properly (which can be tricky), it's a DOA part, or something was damaged during the repair. The keyboard backlight cable is separate from the keyboard connector cable.
I would double-check the keyboard connector cable to make sure it is seated fully and has the piece of anti-static tape to hold it in place. If that doesn't resolve the issue, then you may have a bad part or have damaged the connector.
Hope that helps,
C