On my '03, near fuel filter, below it, there is a three wire(purple, Black w/white stripe, white w/ black stripe) plug that is capped off, what is this? It is shaped like the four prong trailer harness, is it the brake box plug? thank yall

 

Sounds like your talking about the Data link.

 

Data link it is, my Quad plugs into it. I got a letter from Quad and all of the Xzillaraiders made latly(?) do not need that plug anymore.

 

not only is it not needed, but the quad box you have can go in for a quick 6 day turnaround and switch to a tps wire tap setup, a lot less problems and a cleaner signal to use.