Mercury Mountaineer Headlight Switch
Ways to Diagnose a Bad Mercury Mountaineer Headlight Switch
When your headlights are not working, the problem may not lie in the component itself. Sometimes, your Mercury Mountaineer headlight switch may fail too. If your headlight assembly does not come on or if the instrument-cluster illumination does not work, then it is very likely that the switch is bad. The good news is you don't need any expensive tools for troubleshooting. Just get a multimeter and a jumper wire and you can easily find the cause of the component's failure.
Checking the headlight circuit's power
If your headlights are not powering up and you think that the headlight switch is at fault, the first thing you should do is to check the headlight circuit's power. This circuit is the red wire known as circuit C, and it is the one found inside the switch. All you have to do is to make sure that it is getting power in the form of 12 volts. It is important to note that the power here is always present even if you remove the key from the ignition switch. When you probe the front to the headlight switch connector, practice caution and avoid damaging the metal female terminal with the multimeter lead. If you don't want to risk this, back probe the connector instead, or use a wire piercing probe. Once you start probing and the multimeter registered 12 volts, then this part is okay. If it did not register 12 volts, re-check all the connections and test the component again.
Jumper the two headlight circuits together
Once you have confirmed that there is power in circuit C, the next step is to use a fused jumper wire to manually jumper circuit G (the yellow wire) and circuit C together. Before doing this, first disconnect the headlight switch. Once you have located the terminals C and G, jumper them together. Be careful not to damage the terminals so badly that they will permanently open up, resulting in a false contact. When you jumper the two, the headlights should come on. If they do, then these indicate that the headlight switch is bad and needs to be replaced. If they don't, then something else might be causing the headlights to fail.