where is the headlight relay for a 2002 buick reagle

I do not know specifically, but there should be a box in the engine compartment with relays and fuses. There is usually a decal on the inside of the top of that box that identifies all the components, so that should help you find the headlight relay

On my 2004 Buick Regal, high beams worked, but low beams did not. All electrical systems showed power, especially the headlights. Had to replace the dimmer switch.