What is the low beam headlight bulb size for a 1978 Mercury Cougar?

The 1978 Mercury Cougar 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 1978 Mercury Cougar?

The high beam bulb size for the 1978 Mercury Cougar is H4651.

Why are my 1978 Mercury Cougar headlights dim?

Dim headlights on a 1978 Mercury Cougar 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 1978 Mercury Cougar fog light?

The 1978 Mercury Cougar 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 1978 Mercury Cougar single or dual beam?

The 1978 Mercury Cougar uses a dual bulb headlight system. This means you have separate bulbs for high and low beams.

Can I install LED bulbs on my 1978 Mercury Cougar?

Yes, the 1978 Mercury Cougar 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 1978 Mercury Cougar change headlight bulb sizes from the previous year?

Yes — the 1978 Mercury Cougar uses different bulb sizes than the 1977 model. The 1978 generation introduced this bulb configuration.

Is the 1978 Mercury Cougar the first or last year to use H4656 bulbs?

The 1978 Mercury Cougar is the only year in the 1978 generation to use the H4656 bulb for the low beam headlight.

How do I change the headlight on a 1978 Mercury Cougar?

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 1978 Mercury Cougar?

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 1978 Mercury Cougar 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 1978 Mercury Cougar?

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 1978 Mercury Cougar has a unique bulb configuration not shared with adjacent model years.

Fitment Guaranteed for 1978 Mercury Cougar

What Size Bulbs Does a 1978 Mercury Cougar 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 1978 Mercury Cougar Have?

When it comes to nighttime visibility, the 1978 Mercury Cougar 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. This model belongs to the mid years of the Cougar's 1967-2002 production span.

Can You Put LED Bulbs in a 1978 Mercury Cougar?

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.

1978 Mercury Cougar Bulb Size Chart

Position	Bulb Size	Shop
Turn Signal Front	1157A	Buy 1157A →
Side Marker	194	Buy 194 →
High Beam	H4651	Buy H4651 →
Low Beam	H4656	Buy H4656 →
License Plate	168	Buy 168 →
Brake Light	1157	Buy 1157 →
Turn Signal Rear	1157	Buy 1157 →
Tail Light	1157	Buy 1157 →
Parking Light	1157A	Buy 1157A →
Reverse Light	1156	Buy 1156 →

How do the 1978 Mercury Cougar's bulbs compare to other years?

The 1978 Mercury Cougar changed bulb sizes from 1977. The previous model year used a different configuration.

The 1979 model switched to a different bulb configuration.

This bulb configuration covers the 1978 model years. ← 1977 1979 →

Finding the best installation guide...

Other Cougar Years

2002 2001 2000 1999 1997 1996 1995 1994 1993 1992 1990 1986 1985 1983 1980 1979 1977 1976 1975 1974 1973 1972 1971 1970 1969 1968 1967

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