I think that piece might be one out of a pre-99 gt mustang that didnt have TC. But i dont think that looks like what i have for a TC button plug, but it might be different for your model year as it was the first mustang with traction control.

 

Thanks for all the advice/info guys. This is really blowing my mind how the car can clearly have TC without the TC on/off switch.

If anyone with a 99 happens upon this thread and could take a minute to pop off (literally, it snaps right out) the plastic shift bezel to see what their TC switch is connected to that would be greatly appreciated. I've found a few parts cars that have a switch and bezel that should fit if that is in fact all I need to fix it.

 

my 99 v6 has the same plastic bezel as yours because it does not have traction control, im positive a new plastic bezel was put there and whoever did it didnt put the correct one on...a friend of mine has a 99 with traction control and it looks like that picture posted with the trac button...

on my 04 GT that harness looks a lot like my trac control harness from what i can remember, ill tell u this for sure, my 99 v6 does NOT have that harness comin out next to the cig lighter, and since mine doesnt have trac control and yours does id pretty much assume thats your trac control harness, congrats detective youve done it =] now get a the correct bezel and a button lol