Why did both headlamps go out at the same time after having an oil change?

You would need to look at a wiring diagram to see what all is involved in the Headlamps circuit . Some vehicles have a relay controlled by a BCM - body control module or a lighting control module ,totally integrated power module etc.. The Headlamp switch would be a low voltage input to the module in charge ,then the module supplies a ground energizing the headlamp relay . Some of these system can be complex ,an a scan tool may help cut through the diagnostic time.

There is no relay for the headlamps on your Taurus . The lamps have constant B+ voltage , the fuses supply B+ right to the headlamps . The Voltage then travels to the dimmer an flash to pass switch on the steering column , then to the headlamp switch . When you turn on the headlamps the B+ voltage then goes to ground through the headlamp switch ! Pull the headlamp switch an test for B+ voltage on the red with yellow stripe wire . If you do your switch is bad . Go to www.bbbind.com/ for free wiring diagrams , then go to youtube an check out videos on headlamp not working trouble shooting ! From practical experience I'd say there is a problem with the headlamp switch , but don't guess test !

Bad ground loose connection

Lamps, Parking Front Lamp-Lamp Assembly, Taurus
Removal and Installation

1. Remove Headlamp (13008) as outlined.
   

Headlamp Assembly
Removal and Installation

1. WARNING: THE REPLACEABLE HALOGEN HEADLAMP BULB CONTAINS GAS UNDER PRESSURE. THE HALOGEN HEADLAMP BULB MAY SHATTER IF THE GLASS ENVELOPE IS SCRATCHED OR THE HALOGEN HEADLAMP BULB IS DROPPED. HANDLE HALOGEN HEADLAMP BULB CAREFULLY. GRASP HALOGEN HEADLAMP BULB ONLY BY ITS PLASTIC BASE. AVOID TOUCHING GLASS ENVELOPE. KEEP HALOGEN HEADLAMP BULB OUT OF REACH OF CHILDREN.
   Position headlamp switch (11654) and headlamp time delay switch (13736) in the OFF position.
   

1. Remove two bolts retaining headlamp (13008) to upper support assembly and loosen pinch bolt. Remove headlamp assembly from vehicle.
   

1. Remove park lamp bulb and socket (Sable only) and headlamp bulb and socket from Headlamp Assembly as outlined.
   
   
   Headlamp Assembly (Taurus Shown, Sable Similar)
   
   
   
   

1. Turn lamp socket and wiring (13410) assembly 1/2 turn counterclockwise and remove from parking lamp (13200) housing.
   

1. Remove screw from park/turn signal housing.
   

1. Using 1/4 inch drive socket extension and swivel, insert tool through two access holes in upper radiator support. Remove screws from park/turn signal housing.
   

1. Remove parking lamp from vehicle.
   

1. To install, reverse Removal procedure.
   
   
   Front Lamp-Lamp Assembly, Taurus
   
   
   

Have you tried to change the headlights?

REMOVAL & INSTALLATION Sealed Beam NOTE: If vehicle is equipped with headlamp doors turn the headlight switch ON. Open the hood and locate the power distribution center. This center is located in the front of the left front strut tower. Remove the cover from the center and remove the Headlamp Close Relay. This will prevent the headlamp doors from closing to provide easier servicing. Turn the headlight switch to OFF, then perform this repair.

1. Remove the headlight bezel.
2. Unhook the spring from the headlight retaining ring if so equipped.
3. Unscrew the retaining ring and remove it. NOTE: Do not disturb the two long aiming screws. Conventional and Halogen headlamp sealed beams units are interchangeable in pairs, but it is recommended that they not be mixed together (one halogen and one conventional). It is fine to upgrade from conventional bulbs to halogen, but do not change from halogen bulbs to conventional bulbs, especially if the vehicle came equipped with halogen bulbs.
   
4. Unplug the old sealed beam from the engine electrical wiring harness.
5. Extract the old bulb from its mounting bracket. To install:
   
6. Connect the replacement bulb and install it into the receptacle (check operation of headlight before completing repair).
7. Install the retaining ring and secure it in place with the retaining screws. Connect the spring.
8. Install the headlight bezel.

Aero Headlamp Aero headlamp systems use replaceable halogen bulbs that are mounted in aerodynamic, molded plastic lens reflector assemblies. NOTE: Lens fogging is a normal condition and does not require service, as moisture will vent from tubes behind the lens on Aero headlamp-type system. EXCEPT PREMIER AND MONACO It may be necessary to remove the entire headlamp assembly if enough access cannot be gained otherwise.

1. Locate and remove the wire connector behind the headlamp assembly in the engine compartment. It may be necessary to remove certain items in the engine compartment to gain access to the bulb wires.
2. Rotate the bulb retaining ring counterclockwise 1?4 turn and remove the ring, bulb and bulb holder from the lens assembly. The bulb holder has alignment notches. NOTE: Do not touch the bulb with bare fingers or any possibly oily surface, since reduced bulb life may result! Fig. 1: To remove the light bulb, first unplug the headlight electrical connector, then . . .
   Fig. 2: . . . remove the light bulb socket retaining ring
   Fig. 3: Rotate the light bulb socket 1?4 turn counter-clockwise, then pull it straight out of the lens assembly
   To install:
   
3. Wearing gloves or holding the replacement bulb with a cloth rag to keep oil off of the bulb surface, insert the bulb into the rear hole of the headlamp assembly. Make certain that the alignment grooves and tabs line up, push the light bulb into the assembly until seated flush, then turn the bulb clockwise 1?4 turn.
4. Plug the electrical light bulb wiring harness into the new light bulb. Install any items removed from the engine compartment.

PREMIER AND MONACO Unlike the other vehicles covered by this manual, the removal and installation of the headlamp bulbs in the Premier and Monaco models requires the extraction of the entire headlamp lens assembly.

1. Remove the grille-to-headlamp assembly attaching screws.
2. Disconnect the headlamp aiming cable from the aiming screw end.
3. Remove the headlamp assembly attaching bolts from above and behind the lamp assembly and separate the lamp assembly from the vehicle.
4. Unplug the headlamp wire connector. NOTE: Do not touch the bulb with bare fingers or any possibly oily surface, since reduced bulb life may result!
   
5. Rotate the socket counterclockwise 1?4 turn and pull the socket from the back of the lens assembly. Fig. 4: Remove the bezel retaining screws to loosen the headlamp assembly - Premier and Monaco
   Fig. 5: Detach the headlamp wire connector - Premier and Monaco
   Fig. 6: Once the headlamp assembly has been removed from the vehicle, the various light bulbs can easily be removed - Premier and Monaco
   To install:
   
6. Wearing gloves or holding the replacement bulb with a cloth rag to keep oil off of the bulb surface, insert the bulb into the rear hole of the headlamp assembly. Make certain that the alignment grooves and tabs line up, push the light bulb into the assembly until seated flush, then turn the bulb clockwise 1?4 turn.
7. Plug the headlamp wire connector back into the headlamp bulb.
8. Install the assembly into the vehicle and secure in place with the mounting bolts.
9. Connect the headlamp aiming cable to the aiming screw end.
10. Install the grille-to-headlamp assembly attaching screws.

1. Raise the hood.
2. Lift upward on the headlamp retainer (1).
3. Pull the headlamp assembly outward enough to release the headlamp assembly from the upper fascia support.
4. Position the headlamp assembly away from the vehicle body to access the electrical connector
   1. Disconnect the electrical connector from the headlamp assembly.
   2. Remove the headlamp assembly from the vehicle.
   3. Use caution handling halogen bulbs. Remove the headlamp bulb/socket from the headlamp, by turning counterclockwise. CAUTION: Refer to Halogen Bulb Caution in Service Precautions.
   4. Remove the headlamp bulb/socket from the headlamp assembly.

poss very low trans oil level/trans oil needs replacing.
lo cost service centres are good at missing this out.

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GM Century/Lumina/Grand Prix/Intrigue 1997-2000 Repair Guide
Headlamps REMOVAL & INSTALLATION
Sealed Beam

1. Open the hood.
2. Disconnect the negative battery cable.
3. Remove the headlamp bezel retainers and bezel.
4. Remove the spring from the bottom edge of the headlamp assembly.

NOTE Do not apply pressure to the plastic bubble of the vertical aim indicator.

1. Detach the electrical connector from the assembly.
2. Unfasten the two screws from the headlamp retaining ring.
3. Rotate the retaining ring away from the headlamp.
4. Remove the headlamp from the vehicle.
   

To install:

1. Position the headlamp and retaining ring and secure with the two retaining screws. Tighten the screws to 18 inch lbs. (2 Nm).
2. Attach the electrical connector to the assembly.
3. Install the spring to the bottom of the headlamp assembly.
4. Install the headlamp bezel and retainers.
5. Connect the negative battery and test the lights for proper operation.

Composite Headlamps
The headlamps used on the majority of vehicles covered by this guide are called "composite lamps". Unlike the glass sealed beam units used on older vehicles, these headlamps are made of special plastic using small halogen gas bulbs. The bulbs are replaceable, but they do require special handling.

CAUTION Halogen bulbs contain a gas under pressure. Handling a bulb improperly could cause it to shatter into flying glass fragments. Always allow the bulb to cool before removal. Always use the following precautions to help avoid personal injury.
Turn the light switch OFF and allow the bulb to cool before changing bulbs. Leave the switch OFF until the bulb replacement procedure is complete.
Always wear eye protection when changing a halogen bulb.
Handle the bulb only by its base. Avoid touching the glass. Do not drop or scratch the bulb.
Keep the bulb away from moisture.
Place the used bulb in the new bulb's carton and dispose of it properly. Keep halogen bulbs out of reach of children.
Depending on the installation, the low-bean and the high-beam halogen bulbs may actually be removable without removing the entire composite headlamp assembly. Look your application over carefully to see there is enough room behind the headlamp to fit your hand to remove the bulb holder. Since removing the composite headlamp assembly is not difficult, the following procedure assumes that the headlamp is being removed from the vehicle for halogen bulb service.

1. Raise the hood and look at the headlamp installation. On some applications, the headlamp is retained by screws and some molded tabs that slip into slots in the sheetmetal mounting bracket. On other applications, two U-shaped clips may hold the headlamp in place. Remove the headlamp retainers and gently work the headlamp free of the vehicle.
2. If the wiring harness is so short that it is difficult to work on the headlamp, simply unplug the electrical connector from the headlamp assembly.
3. The halogen bulb may have a large, knurled plastic ring that retains the socket to the headlamp. Turn this ring to detach it and remove the socket with the halogen bulb.
4. Remove the burned-out bulb and discard safely.

WARNING Do not touch the glass bulb with your fingers. Oil from your fingers can severely shorted the life of the bulb. If necessary, wipe off any dirt or oil from the bulb with rubbing alcohol before completing installation.

1. Take great care not to touch the new replacement halogen bulb as oil from your skin will burn when the bulb is turned on and may damage the glass, shortening the life of the bulb. Use a clean, dry paper towel to handle the bulb.
2. Installation is the reverse of the removal procedure.
3. Verify that the lights work correctly.

Headlamp adjustment may be temporarily made using a wall, as described below, or on the rear of another vehicle. When adjusted, the lights should not glare in oncoming car or truck windshields, nor should they illuminate the passenger compartment of vehicles driving in front of you. These adjustments are rough and should always be fine-tuned by a repair shop which is equipped with headlamp aiming tools. Improper adjustments may be both dangerous and illegal.




Fig. Typical composite headlamp aiming rods





Fig. Typical horizontal and vertical adjuster locations




Fig. Vehicle headlamp aiming device (RH)-Buick shown, others similar
Before removing the headlamp bulb or disturbing the headlamp in any way, note the current settings in order to ease headlamp adjustment upon reassembly. If the high or low beam setting of the old lamp still works, this can be done using the wall of a garage or a building:

1. Park the vehicle on a level surface, with the fuel tank about 1 / 2 full and with the vehicle empty of all extra cargo (unless normally carried). The vehicle should be facing a wall which is no less than 6 feet (1.8m) high and 12 feet (3.7m) wide. The front of the vehicle should be about 25 feet from the wall.
2. If neither beam on one side is working, and if another like-sized vehicle is available, park the second one in the exact spot where the vehicle was and mark the beams using the same-side light. Then switch the vehicles so the one to be aimed is back in the original spot. It must be parked no closer to or farther away from the wall than the second vehicle.
3. Perform any necessary repairs, but make sure the vehicle is not moved, or is returned to the exact spot from which the lights were marked. Turn the headlamps ON and adjust the beams to match the marks on the wall.
4. Have the headlamp adjustment checked as soon as possible by a reputable repair shop.

Hope helps with this (remember rated this) Good luck.

Caution Halogen bulbs contain gas under pressure. Handling a bulb improperly could cause it to shatter into flying glass fragments. To help avoid personal injury:
Turn off the lamp switch and allow the bulb to cool before changing the bulb.
Leave the lamp switch OFF until the bulb change is complete. Always wear eye protection when changing a halogen bulb. Handle the bulb only by its base. Avoid touching the glass. Keep dirt and moisture off the bulb. Properly dispose of the used bulb. Keep halogen bulbs out of the reach of children.
Raise the hood.
Remove the headlamp assembly bolts from the upper fascia support.
Slide the headlamp assembly outward enough to release the headlamp bracket tabs from the slots in the upper fascia support.
Position the headlamp assembly away from the vehicle body to access the electrical connector.
Disconnect the electrical connector from the headlamp assembly.
Remove the headlamp assembly from the vehicle.
Disconnect the electrical connector from the headlamp bulb/socket.
Remove the headlamp bulb/socket retainer ring from the headlamp, by turning counterclockwise.
Remove the headlamp bulb/socket from the headlamp assembly.

Headlamp Assembly Removal

1. Remove radiator air deflector from radiator support.
   

1. Remove two screws and two nuts retaining headlamp door (13064).
   

1. Pull headlamp door from vehicle. Remove three bulbs and sockets.
   

1. Disconnect engine control sensor wiring (12A581) from headlamp bulb (13007).
   

1. Remove two retainers attaching upper two attachments of headlamp (13008).
   

1. Turn horizontal headlamp adjusting screw (13032) completely out of the adjusting nut.
   

1. Pull headlamp from vehicle.