Tonight I removed the dash bezel in my 05 to reinstall the rattling aftermarket stereo
there was two plugs attached to the headlight switch
The long flat one was for the headlight switch but the smaller square one just plugs into a empty hole
I am assuming the little square plug is for fog lights ??

 

I believe it is for fog lights, But I am not 100%

 

Yes that is for factory fog lights, all blazers have the wiring but not all of blazers computers are capable of actually using them.