I need help with a wiring harness

Ok bit of a lengthy question. I have a 2000 ford f150 4.2l V6 5 speed 143k Miles. Kinda a frienstien truck it have a dash from a different vehicle. And after a couple years of owning the truck it started to have spark knock. And when I took it to the local mechanic he showed me and told me that my ECU had a bad pin which cause cylinder 1 to not have spark which the previous owner or the owner before him had known (didn’t disclose) but that’s beside the point. (First truck being a first truck I figured oh well shit happens.) But they had piggy back off of cylinder 4. So when 4 fires 1 fires. Causing cylinders 1/4 to be lean. I was hoping to replace the harness because he used god forsaken scotch locks (which can burn in hell) but I can’t for the life of me find a used or OEM replacement for the 4.2l V6. Does anyone know what I should do? Please and thank you.