Typically with electronic repair, it's bad practice to power on the device when repairing. The cool thing about the Taptic Engine is that the one from the iPhone 8 should be compatible with the iPhone SE as they should be the same. I'd also use [guide|133892|the guide from iFixit|new_window=true] just to make sure that your bases are covered. You'll be looking at steps 18 through 23. Also, make sure that your battery itself is secure, as a bad adhesive job could be causing the issue.