I've had a good deal of problems with my car due to the remote starter I had installed last month. Every place (3) I brought it, the service techs called me up asking what the small battery was doing under the hood and about the mass of wires run through the firewall.
So, I explain what it's for and what connections I have made to the electrical system, yada yada yada.
My point is that it may help put people at ease if you have some sort of circuit diagram to go with your install. These things are complex and the last thing a guy needs to do is try to figure out wiring that's not in the service manuals. And, it would help the lawyers out when you sue the shop for not honoring your transmission warranty because of an LCD screen.