Chevrolet Repair: Electric dim switch or relay, gm tech 2, daytime running lights

Question
I have a 2002 Chevrolet s-10  .
You know when you turn your headlights on your radio dims.

Well when I start my engin the radio is dimmed without the headlights being turned on and the headlights are on high beam.  Then I play with the dome override button the headlights go back to daytime running lights and the radio brightens up the way it suppose to.

I changed the headlight switch unit. It did not fix the problem.

Is there a relay located somewhere?    And where is it locate?

If not, what could my problem be?

Answer
HI NEIL,,I AM NOT AT WORK TODAY BUT, I THINK THIS TRUCK HAS A LIGHT SWITCH MODULE THAT CONTROLS THIS FUNCTION OR IT MAY GO THROUGH THE BCM[ BODY CONTROL MODULE.]THIS IS NOT A RELAY PROBLEM..MY GUESS IS THE BCM IS GETTING FAULTY..DO YOU HAVE ANYONE IN YOUR AREA THAT HAS A GM TECH 2 SCAN TOOL TO GET INTO THE BCM TO CK ?? THIS WILL BE THE EASIEST WAY TO DIAGNOSE. THEY CAN MANUALLY TURN THIS ON FROM THE SCAN TOOL AND SEE IF IT WORKS LIKE THIS..I HOPE THIS HELPS YOU,LET ME KNOW IF YOU NEED MORE INFO..PLEASE WHEN YOU LEAVE THIS SITE WOULD YOU MIND RATING MY ANSWER.GOOD OR BAD. THANK YOU,, TOM.