I thought it was standard on the GT's...
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It was, but only for certain years and packages.
Back in 1999 and 2000, ABS and traction control were two different options. You had to get ABS however, before you could get TC
Around 2001 or 2002, they became a package so you got ABS and T/C together. Depending on the year it was optional on GT deluxes and standard on GT premiums.
For 2004, ford made it optional on all models of 2004 GT. It was an $800 option, and not a lot of dealers got it so a lot of 2004's out there have neither ABS nor traction control.
SO if your 2004 doesn't have the T/C button, you don't have ABS as well.
I must be the only one that likes T/C. I leave mine on during normal driving. It's not like i drive around ripping through the gears spinning tires. When i'm on daily driving routines, it stays on and never gets tripped. In the rain, i leave it on as well since it's saved me a few times. If it's dry and sunny out and i feel like having fun, i turn it off.