GMC P3500 Headlight Dimmer Switch Guide: 1979-1989
Having trouble switching from low to high beams? Your floor-mounted dimmer switch is the likely cause.
- The dimmer switch on a 1979-1989 P3500 is a simple, foot-operated button on the floor.
- Failure symptoms are direct: headlights get stuck on one beam or won't switch.
- Replacement is very easy, inexpensive, and can be done in under 30 minutes with basic tools.
- Quality aftermarket brands like Standard Ignition offer reliable, direct-fit replacements.
Is Your Headlight Dimmer Switch Failing?
The headlight dimmer switch on the 1979-1989 GMC P3500 is a durable, simple part, but after decades of being stepped on, it can wear out. Failure often comes from internal corrosion or mechanical wear. Symptoms are usually straightforward and point directly to the switch.
Common Symptoms of a Bad Dimmer Switch:
- Stuck Beams: Your headlights will be stuck on either low or high beams and won't switch when you press the floor button.
- No Headlights: In some cases, a complete failure of the switch can prevent both high and low beams from turning on at all.
- Intermittent Operation: The switch might work sometimes and not others, or you may notice the headlights flicker when you press the button.
Safety First
A faulty dimmer switch is a serious safety hazard. If you cannot switch between high and low beams, your visibility is compromised, and you could endanger other drivers. Do not drive at night if your headlights are not functioning correctly.
Choosing a New Aftermarket Dimmer Switch
For a vehicle like the P3500, original equipment (OEM) parts from GM are likely discontinued. Fortunately, the aftermarket offers reliable and affordable replacements that meet or exceed original specifications.
The primary brand available for this part is Standard Ignition (Standard Motor Products). SMP is a long-standing company founded in 1919, known for producing quality replacement parts. Their dimmer switch (part number DS72) is a direct-fit replacement and receives positive reviews for its fit and function. Other brands like AC Delco and Wells also offer compatible switches. Given the simplicity of the part, a switch from any of these reputable brands is a solid choice.
Pro Tip: Check the Connector
When you replace the switch, inspect the wiring connector. After many years, the plastic can become brittle and the terminals can corrode. If the connector is damaged, it should be replaced to ensure a solid electrical connection.
Headlight Dimmer Switch Replacement Cost
Replacing the dimmer switch is one of the more affordable repairs you can make. The part itself is inexpensive, and labor is minimal due to its easy accessibility.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Switch | $15 - $30 |
| Shop Labor | $50 - $100 |
| Total Estimated Cost | $65 - $130 |
Frequently Asked Questions
Where is the dimmer switch located on my P3500?
The headlight dimmer switch is mounted on the floor, to the left of the brake and gas pedals. You will need to pull back the floor mat or carpet to access the two screws holding it in place.
Can I replace the dimmer switch myself?
Yes, this is a very DIY-friendly repair. It typically requires only basic hand tools to remove two mounting screws and unplug a single electrical connector. The entire job can often be done in 15-20 minutes.
Are there any recalls for the headlight dimmer switch on my truck?
No, there are no specific recalls or technical service bulletins (TSBs) from the NHTSA for the headlight dimmer switch on the 1979-1989 GMC P3500. Recalls for GM headlight issues you may find online are for much newer vehicles and different components.
Could my problem be the main headlight switch on the dash instead?
It's possible, but less likely if your other lights (like parking lights and dash lights) work correctly and the only problem is switching between high and low beams. If wiggling the turn signal stalk or pressing the floor switch causes the lights to flicker or change, the floor dimmer switch is the most probable cause.
Technical Specifications
Location: Floor Mounted, Terminal Quantity: 3, Terminal Type: Blade
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.