Alright, ford must like to leave extra plugs around cause I've never seen a 4 banger GT lol. VIN does say GT so it's not a body kit.
What I'm really curious about is the inline fuse in one of the pictures. It's attached to an orange with blue stripe wire. I can't tell where the other end goes though.
PM me your email address and I will send you a complete Ford Factory 89 Mustang electrical diagram set. The zip file is 2.5 MB and is too big to fit through Stangnet's email gateway.
89 Mustang wiring diagrams zip package–
They are in a zip file format to reduce the size of the package. If you don't have Windows 7 or Windows 8, you’ll need WinZip or other Windows archive tool to extract them from the zip file.. See www.majorgeeks.com - Download Freeware and Shareware Computer Utilities for a free download.
The diagrams show the location area and the connectors are drawn to the same shape as those in the car.