What is the low beam headlight bulb size for a 1979 Mercury Grand Marquis?

The 1979 Mercury Grand Marquis uses a H4656 bulb for the low beam headlights. We recommend upgrading to LED for better visibility.

What is the high beam headlight bulb size for a 1979 Mercury Grand Marquis?

The high beam bulb size for the 1979 Mercury Grand Marquis is H4651.

Why are my 1979 Mercury Grand Marquis headlights dim?

Dim headlights on a 1979 Mercury Grand Marquis can be caused by aging halogen bulbs, which lose brightness over time, or oxidation (cloudiness) on the plastic headlight lenses. Upgrading to a H4656 LED conversion kit can provide a significantly brighter and whiter light output.

Which bulb fits the 1979 Mercury Grand Marquis fog light?

The 1979 Mercury Grand Marquis typically does not come with factory fog lights in all trim levels. If your vehicle is equipped with them, check the manual as sizes can vary by trim.

Is the 1979 Mercury Grand Marquis single or dual beam?

The 1979 Mercury Grand Marquis uses a dual bulb headlight system. This means you have separate bulbs for high and low beams.

Can I install LED bulbs on my 1979 Mercury Grand Marquis?

Yes, the 1979 Mercury Grand Marquis comes with standard halogen bulbs from the factory, but they can be upgraded to LED. You will need a H4656 LED conversion kit for the low beams.

Did the 1979 Mercury Grand Marquis change headlight bulb sizes from the previous year?

Yes — the 1979 Mercury Grand Marquis uses different bulb sizes than the 1978 model. The 1979 generation introduced this bulb configuration.

Is the 1979 Mercury Grand Marquis the first or last year to use H4656 bulbs?

The 1979 Mercury Grand Marquis is the only year in the 1979 generation to use the H4656 bulb for the low beam headlight.

How do I change the headlight on a 1979 Mercury Grand Marquis?

Turn off the vehicle and open the hood. Locate the headlight assembly from behind, remove the dust cover or retaining clip, disconnect the wiring harness, twist the old H4656 bulb counter-clockwise to remove it, then insert the new bulb and reassemble. The whole process typically takes 10 to 30 minutes per side depending on accessibility.

Are LED headlights legal for a 1979 Mercury Grand Marquis?

LED bulbs used off-road or in auxiliary lights are legal everywhere. For on-road headlight use, legality varies by state. Many states allow LED retrofits as long as the beam pattern meets DOT standards. For the best legal compliance, choose a DOT-approved H4656 LED kit that is designed as a direct replacement and produces a proper cutoff pattern without excessive glare.

How much does it cost to replace 1979 Mercury Grand Marquis headlights?

A pair of halogen H4656 bulbs costs $15 to $40, while LED conversion kits run $25 to $60 per pair. If you have a shop do the work, expect an additional $20 to $50 in labor per bulb. Replacing them yourself at home saves the labor cost and usually takes under 30 minutes.

What is the difference between halogen and LED for a 1979 Mercury Grand Marquis?

Halogen bulbs produce a warm yellow light (around 3200K), last 500 to 1000 hours, and draw more power. LED bulbs emit a brighter white light (5000-6000K), last 25,000+ hours, and use less energy. LED upgrades for the H4656 position are available as direct plug-and-play replacements.

The 1979 Mercury Grand Marquis has a unique bulb configuration not shared with adjacent model years.

Fitment Guaranteed for 1979 Mercury Grand Marquis

What Size Bulbs Does a 1979 Mercury Grand Marquis Use?

Correct headlight, fog light, and tail light bulb sizes. Sourced from OEM catalog data.

Installation Difficulty

Easy (Plug and Play)

Est. Replacement Cost

$15 - $40 (Halogen) / $30+ (LED)

What Lighting System Does the 1979 Mercury Grand Marquis Have?

When it comes to nighttime visibility, the 1979 Mercury Grand Marquis relies on an arrangement of 10 specialized bulbs. It features a comprehensive lighting system powered by a dual-bulb halogen configuration using separate H4656 low beam and H4651 high beam bulbs for precise light distribution.

Can You Put LED Bulbs in a 1979 Mercury Grand Marquis?

Upgrading to LED is one of the most effective ways to modernize your Mercury's appearance and safety profile. We recommend starting your upgrade with the H4656 low beams, as they see the most use. Adding a matching H4651 LED kit later will complete the look and ensure consistent lighting performance.

1979 Mercury Grand Marquis Bulb Size Chart

Position	Bulb Size	Shop
High Beam	H4651	Buy H4651 →
Low Beam	H4656	Buy H4656 →
Turn Signal Front	1157A	Buy 1157A →
Turn Signal Rear	1157	Buy 1157 →
Tail Light	1157	Buy 1157 →
Side Marker	1157	Buy 1157 →
Reverse Light	1156	Buy 1156 →
License Plate	168	Buy 168 →
Brake Light	1157	Buy 1157 →
Parking Light	1157A	Buy 1157A →

How do the 1979 Mercury Grand Marquis's bulbs compare to other years?

The 1979 Mercury Grand Marquis changed bulb sizes from 1978. The previous model year used a different configuration.

The 1980 model switched to a different bulb configuration.

This bulb configuration covers the 1979 model years. ← 1978 1980 →

Finding the best installation guide...

Other Grand Marquis Years

2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994 1993 1990 1986 1985 1983 1980 1978 1977 1976 1975

More from Mercury

Bobcat Breezeway Brougham Caliente Capri Colony Park Comet Commuter

Other Vehicles That Use H4656 Bulbs

1992 Chevrolet Camaro 1992 Chrysler New Yorker 1991 Chevrolet G10 1991 Chevrolet Van 1991 Chrysler LeBaron 1991 Ford Country Squire