This thread was a life saver. I had this exact same problem after changing out badly swollen battery on 2017 MBP. My trackpad and keyboard worked fine before battery change but stopped working after new battery installed and both fans going full speed non-stop. Did all the resets and recommendations but nothing worked. Took to two different “computer fix it” places who told me 2017 “tough to repair” (?) and that I “probably” needed a new logic board. I found this thread and ordered a new trackpad with ribbon on ebay. Just installed and it fixed everything. MBP back to normal. What a life saver.