which wire(s) can I tap into that are hot with either accessary on or ignition
turned to on, start etc. Which wire running from the factory brake controller
plug is a 12v hot? Could I tap into the hot wire from the 4 pin connector that
I used for a power source to my pyro gauge? I obviously know nothing about
wiring.

 

btw its a 99,powerstroke

 

What is it that you are wiring in? Most any circuit in your truck will either be a constant hot, or keyed hot. The most notable exception would be the lights circuits, which are a switched constant.

Finding out which wire is hot when is a simple matter, just go to your favorite auto parts place and get a test light. They're very easy to use and are beneficial in helping you to understand how your electrical system works.

 

yeah, I think I'll borrow one this weekend, I should buy one tho cuz eventually I
will need one. I'm trying to re-wire my brake controller.