what cause parking light to go off when applying the brakes

It sounds like someone robbed the power from your parking lights to gain power to the brake lights. So when you hit the brakes, all the power goes to the brake lights which will cause the parking lights to dim or go out. Just a guess here. Did you just recently aquire this car? Or have you owned it for some time and this has just started happening?

This is a common problem on some vehicles. It is caused by broken or loose ground. The park lights will ground through the brake light circuit until brakes are applied. Check the ground cables for your parking lights. ***** It's a very old question but I had to answer it as it may help somebody out there ******