DRL problem - Headlamps

Hello! I have a 2002 S10 Blazer. The problem is that when I start the truck, day or night, the fog lights come on but no low beam. I have to switch to high beam to get any lights at all. During the day the DRL come on "sometimes" after driving a while but as soon as I put it in "Park" they go off. The did stay on until the key was turned off. Have checked all the fuses and relays under the hood and on the side of the dash. All check out fine. My son has the same make truck. My bulbs and the DRL relay works fine in his truck. Are there any switches I should look at and where would they be located. Haven't a clue where to go from here.
Any suggestions?

i would have the drl senor tested and see if there may have been a recall on it. the sensor is in the top of the dash

Thanks!