Don’t Install Aftermarket GMT800 Headlights Until You Do This

Most aftermarket headlights look great out of the box. The problem is they don’t always stay that way. If you’ve ever installed a fresh set of aftermarket housings on a GMT800 and watched them yellow, fog up, or let moisture in after a season or two, there’s a good chance it was preventable.

Before bolting on a new set, take a few extra minutes and do two things: coat the lens and seal the housing. It’s not complicated, and it doesn’t require any special tools.

Which Trucks This Applies To

This applies to any GMT800 platform with aftermarket headlight housings, including:

• 1999–2006 Chevrolet Silverado (including 2007 Classic)
• 1999–2006 GMC Sierra (including 2007 Classic)
• 2002–2006 Chevrolet Avalanche
• 2000–2006 Chevrolet Suburban and Tahoe
• 2000–2006 GMC Yukon and Yukon XL
• 2002–2006 Cadillac Escalade

If you’re running aftermarket housings on any of these, the same principle applies.

Why Aftermarket Headlights Fail Early

OEM headlight housings are UV-coated at the factory and sealed properly. Most aftermarket replacements skip that step or apply minimal protection. The polycarbonate lens is essentially raw when it leaves the packaging.

Left unprotected, that lens will start to oxidize from UV exposure. You’ll see yellowing first, then haziness, then the interior surface of the lens can fog up once moisture finds its way in through an imperfect seal. At that point you’re replacing them again.

It’s not a knock on all aftermarket brands — it’s just reality with most budget and mid-range housings. A little prep before installation closes the gap significantly.

Step 1: Apply Headlight UV Coating Before Installation

The first thing to do before the housings go anywhere near the truck is protect the lens. Doing this before installation is easier — you can coat the lens fully without worrying about masking bodywork, and you’re not working at an awkward angle.

The product used in this video is Meguiar’s Keep Clear Headlight Coating.

Disclosure: This post may contain affiliate links. If you buy through them, FullSizeChevy may earn a small commission at no extra cost to you.

Meguiar’s Keep Clear Headlight Coating – 4OZ →

It’s a UV-blocking sealant designed specifically for headlight lenses. It goes on easy, dries clear, and adds a layer of protection that the aftermarket housing didn’t come with.

How to apply:

• Wipe the lens down with a clean cloth to remove any dust or oils from packaging
• Apply the Keep Clear coating in thin, even passes overlapping by about 50%
• Two coats is recommended on the can, with 5 minutes dry time between 1st and 2nd coat.
• After 5 minutes it is dry to the touch.
• Let the lights cure 24H fully before installation — don’t rush this step!

This takes maybe 10 minutes on new lenses. Don’t skip it!

Step 2: Seal the Housing Before Install

The second step is sealing the housing itself. Aftermarket headlight housings are assembled with a basic gasket or butyl seal, and it’s often not as tight as OEM. Moisture can work its way in over time — especially on a truck that lives in temperature swings, rain, or road spray.

Before mounting the housing, inspect the seal around the perimeter of the lens and back cap. If it looks thin or inconsistent, run a bead of clear exterior silicone around it. This is a common step on any quality headlight build, and it applies here too.

A properly sealed housing keeps condensation out and keeps the interior of your new housings looking clean long-term.

Watch the Full Walkthrough

The install is done on a GMT800 Silverado and covers both steps in real time.

Installation Notes

A few things worth knowing once you get to the actual install:

• Stock wiring harness connectors should plug straight in on most GMT800 aftermarket housings, but confirm before purchasing — some housings require an adapter
• Aim the headlights after install — aftermarket housings don’t always come pre-aimed and most don’t hold the OEM aim after a swap
• Let the coating cure before you’re back on the road in rain or heavy spray

Final Thoughts

This isn’t a complicated process, but it’s one most people skip because they’re anxious to get the new lights on the truck and move on. Spending an extra few minutes before installation can meaningfully extend the life of the housings and keep them looking better longer.

Aftermarket headlights vary a lot in quality. The coating and seal steps won’t make a cheap housing last forever, but they close the gap on what the factory finish left out.

Frequently Asked Questions

Does this work on any aftermarket headlights or just GMT800?

The process applies to any aftermarket polycarbonate headlight housing. GMT800 is the focus here because it’s a common platform for headlight upgrades, but the same steps apply to other GM trucks.

Can I apply the coating after installation?

Yes, but it’s harder. Doing it before install means you can coat the full lens surface without masking the truck, and you can let it cure flat. If you’ve already installed, mask off the surrounding area carefully and work in sections.

Does Meguiar’s Keep Clear work on existing headlights too?

It’s designed for clear lenses. If your existing headlights have significant oxidation or yellowing, you’d want to wet sand and polish first to restore clarity, then apply the coating to protect what you’ve restored. I would recommend 220-3000 grit in stages for wetsanding if restoring headlights. More on this to come.

Will sealing the housing prevent all fogging?

Sealing reduces the main entry points for moisture significantly. If a housing has a vent tube or breather, that’s intentional — condensation from temperature changes is normal in small amounts and typically clears. Heavy persistent fogging usually means a bad seal somewhere.

What year GMT800 trucks take the same headlight housing?

The 1999–2002 and 2003–2006 Silverado/Sierra use different headlight housings. Confirm your exact year before ordering. The 2007 Classic (sold alongside the new GMT900) uses the GMT800 body and takes the same housings.

Join the Conversation

If you’re working on a GMT800 truck or SUV — whether it’s a lighting upgrade, a full build, or just getting it sorted — join the FullSizeChevy forum and share what you’re doing.

Discuss this in the FullSizeChevy forum →

Post your install photos, share which housings you went with, and let us know if you’ve run into headlight fogging issues on your GMT800.