I have noticed lately at night when the headlights are on, if you roll down the window or anything else that draws power the headlights will dim some during use? What is causing this? The battery tested good and no other issues or codes... wondering why this does it, even when applying the brakes they dim a bit.

 

Only 2 I can think of; battery or alternator.

 

Serpentine Belt, tensioner, connection between alternator and battery. If you have no issues starting then just the wire between the alternator and starter.

 

Dirty contacts in the window switches , is also a possibility, along with corroded ground wires

 

Do this. Put a meter on it and see what is actually going on with voltage and report back.

 

it's not a real problem
a car is not a building, its powersupply is very sensitive. I will say more - the relationship between power consumption and fuel consumption (ie, inverse relationship) is also felt instantly and without the use of special devices.
If the dimming of the headlights is short-term and is expressed in a slight loss of intensity, you can not worry. If, when lowering the glass or turning on the headlights, you suddenly hear or feel a slight increase in the engine speed, do not worry either. A simple redistribution of energies within a closed system.
To illustrate: the constant winter operation of the heater (just a small motor with a fan under the dashboard) increases fuel consumption by up to a liter per 100 km, and the air conditioner affects even more. Additional set of headlights + 0.2 / 0.3 liters per 100 km.
But! .. cleaning contacts and generally inspecting the electrical system is never harmful

 

Yeah no other issues ( starting, windows, ect.... ) the headlights just do a faint fade and back to normal but doesnt do anything while ac kicks on/off or when heat is running as well as heated seats surprisingly but only notice it when braking or window switch is used oddly ?

Belt is good and snug so not slipping and alt is charging properly.

 

So , loose or corroded ground wires

 

Or clogged glass guides, maybe ..
Just a guess, of course: such as the rails are clogged, the window motor is making excessive efforts to raise / lower the window, the increased power consumption of the window regulator takes energy from another nearby consumer.
By the way, you can experiment: put the vehicle at dusk in front of the wall and lower / raise all the windows one by one. You can visually determine the dependence.