Home button works but logic board doesn't see it

I am looking for what part to replace when the home button works but jumping the two prongs by the lighting port will not activate siri or send phone to home screen. I am getting 1.7volts on one prong but even when I short them and get voltage on the other prong the main board doesn't see it. If I take my phone and open it and short the prongs siri pops up. Just wonderinig if its the cable or main board. It did it with original home button intermittently and replacement. Then one day it just quit altogether. Any help would be great thx