my headlights flicker after about 20 mins of having them on . i have changed the headlight switch put a new headlight in also and cleaned the grounds but it still does it.. could some plz help me with this problem

 

Trace the circuit to see if a relay is between the the switch and the lamps. Both lamps are flickering so you're solving for what is in common to both. The ground points are usually separate, the lamps are uniquely different so you're down to the 12V supply. 20 min is a long "burn" time so you're looking for what could be arcing or getting hot after extended time. Points to a relay with a weak coil or carboned-up contacts. They chatter or internally arc causing flicker.

 

Welcome to the site!
Need some more info to help...
Does it do this on low OR high beams?
Do they dim, or flicker, or go off for a few seconds then back on? Which do they do?
Are they stock-type bulbs or some new aftermarket "high output" kind that could draw too much current and trip the circuit breaker in the light switch?

 

What Rob said.

Also, you say your "headlights" flicker, but you "put a new headlight in."
Is this one or both lights, and what made you decide to replace only one?

- Eric