Do coin doors come with wires attached already or some kind of harness or do they come blank and I attach the wires from MY harness in order for it to work?!
Sometimes, but not typically in my experience. I think of all of the coin doors that I have ever purchased (all used), only one had a harness attached (and, since the molex didn't match the harness that I had in the cab, I pulled it).
Expanding on protokatie's question:
Can you provide details as to the coin door that you are looking at and for what purpose (e.g. emulator ... MAME ... cab, etc.) ? Pics are worth their weight in gold.