From inside the engine compartment of your 2005 Pontiac Bonneville, press in on the bulb socket of the bulb you want to replace to disengage the retainer lock. While holding it in, turn the socket counterclockwise and pull it out of the headlamp assembly. Lift the tabs and pull the bulb from the connector. Insert a new bulb -- careful not to touch the glass with your fingers lest you leave skin oils on it that reduce the life of the bulb -- and engage the tabs. Insert the socket into the headlamp assembly. Press the socket in and turn it clockwise until it stops.
To replace the passenger-side high beam bulb, you might need to remove the headlamp assembly. Take out two screws on the top of the headlamp assembly -- note the screws are different lengths -- and then gently pry the assembly forward to disengage the plastic retaining tabs. Change out the bulb, then snap the headlamp assembly back into place. Tighten the screws to 80 inch-pounds.
Your Bonneville takes bulb No. 9006 for the low beams. For the high beams, you'll need bulb No. 9005 for the SE or SLE. The GXP takes bulb No. H1R1 for the high beams.
