A technician will first look to rule out simple causes of malfunctioning headlamps - a blown fuse or a faulty relay. The relay may be removed and tested with a multimeter. Using a diagnostic scan tool, the technician might check the operation of the lighting system by reading data from the Light Control Module. The dimmer switch may be removed and probed with a multimeter to diagnose a problem. The technician will need access to a wiring diagram for the vehicle to determine which wire terminals on the combination switch assembly are used for the dimmer switch.
How are Headlamp Dimmer Switches replaced?
To replace a headlamp dimmer switch, a technician will disable power to the lighting system by disconnecting the battery or by pulling a fuse. The steering column cover trim and lower dash panels need to be removed for access to the switch assembly. In some cases, this can be an extensive operation that includes removal of trim above the steering wheel and around the instrument cluster. The retaining fasteners are unscrewed and the combination turn signal and headlamp switch module is unplugged from the wiring harness and removed as an assembly. The new module is plugged in and put in place and fastened before the trim is installed. The technician will restore power to the system and test the new switch.
RepairPal Recommendations for Headlamp Dimmer Switch issues
If symptoms of a faulty headlamp dimmer switch appear, the entire lighting system should be inspected by a qualified technician at a trusted repair shop. Since relays or control modules can be at fault, it is recommended to have the issue diagnosed before purchasing and replacing the switch.
What to look out for when dealing with Headlamp Dimmer Switch issues
The dashboard trim can be tricky to remove without damaging the panels. On some higher-end vehicles, the trim components can be extremely expensive to replace, and, in some cases, can only be replaced as a complete set costing thousands of dollars. Care should be exercised when disassembling components on the dashboard.
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Disassembly of the dashboard and steering column should probably be left to a professional. A comprehensive inspection of the lighting system that may include a diagnostic scan with a special scan tool should be performed any time there is a problem with the headlamps. The DIY mechanic with a solid understanding of automotive electrical circuit testing can identify the failed switch, but if the switch and relays are serviceable, the vehicle should be referred to a professional.