In my 2001 mustang when its cold I get a whining sound when i turn the wheel or press the brake all the way down. Does anyone know what might cause that.

 

First off, Welcome to The Mustang Source. The question I have is how cold in Texas? Now first off in the morning, most vehicles need to warm up a bit to get the fluids flowing in order to allow for proper motion, such as your steering wheel noise. My daily driver, Mit. Galant does this when it is below 32* here in MO. As for the brake, check booster hose for seating and be sure the system is sealed 100% to prevent air getting in or out of this closed system.

 

When its about 25 degrees outside. I thought maybe it was the power steering pump but it noise is also caused by my brake..

 

Your brake booster is powered off of your power steering. It's called hydroboost. So in a sense you are correct and you are hearing you P/s pump. Once it's warm does it still do it? Most likely it's just that the fluid is very thick because of the cold. If it stops when warm you are ok but if not I'd do a power steering flush and add some Lucas to it

 

I agree with Onesickstang01. Since you have a 2001 I would do a P/S flush with fresh Ford Mercon V (Mercon is OBS) or Mobil1 Full Synthetic. The fluid should be a nice pink color. If is is dark red, brown or black it's time and burnt or contaminated. Do this at 100K then every 50K there after or sooner based upon color. There is a procedure in the Ford manual. You want to get new fluid into the power rack, cooler if equiped and the braking system. If it still whines, then replace the P/S pump.