Quick wiring question
 

New member here, great resource for information you allhave developed. I am about to purchase a 1999 Coupe. I am wondering if anyone knows if the wiring for all the optional accessories is already in the car. For instance, I have a project 1988 Mustang that has all the wiring for the upgrade stereo, speakers, etc. already in behind the dash, just not hooked to anything. So, if I wanted to add say, an HUD system to acoupe not currently equipped, could you just buy the controls and the projector and such and hook it in, same with the dual zone A/C and that sort of thing. I know there's probably individual harnesses for each item, but is the main wiring just sitting there waiting to be used? Thanks.