How do I Troubleshoot a 2004 Mercury Headlight?
- 1). Check which headlights are not turning on. Replace those bulbs that are not turning on, and check them again. If they still do not turn on, continue to the Step 2.
- 2). Prop open the hood, and locate the fuse box on the left side of the engine compartment. Inspect the fuses that control the headlight bulbs that are not turning on, and look to see if they are blown. Replace any that are blown, and turn on the headlights. If the do not work, continue to Step 3.
- 3). Unplug the wiring harness from the rear of the headlight assembly that does not work. Connect the positive lead of your voltmeter to the positive terminal on the car battery, and connect the negative lead of the voltmeter to the power lead of the wiring harness. Verify that power is coming through the harness. If not, replace the harness. Continue to the next step if power is coming through the harness and the headlights still do not work.
- 4). Replace the headlight switch. Disconnect the negative battery cable, and remove the steering column bezel. Disconnect the wiring block from the headlight switch, and verify that the leads on the wiring block are clean. Otherwise, clean them, and try the headlights again. Remove the three screws mounting the headlight switch, if the headlights still do not turn on, and remove the headlight switch. Plug the wiring block into the replacement headlight switch; mount the switch with the screws to the steering column, and check that the headlights now work.
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