GMT800 Tow Package Retrofit: Wiring, Brake Controller & Tow Mirrors (1999–2006)

Plenty of GMT800s left the factory without the tow package, and most of what matters can be added. Trailer wiring, a brake controller, and tow mirrors are all reasonable retrofits. What you can’t easily “add” is a bigger transmission or higher tow rating — those are built into the truck. Here’s the realistic breakdown.

Which trucks this covers

• 1999–2006 Silverado & Sierra, Tahoe, Suburban, Yukon, Avalanche

What the factory tow package included

Depending on year and trim it bundled things like the trailer wiring harness and connector, a heavier-duty setup, and provisions for a brake controller. Knowing what your truck already has (check the RPO codes on the glovebox sticker) tells you what you actually need to add.

What you can retrofit

• Trailer wiring & 7-pin connector: add a proper harness so you have trailer lights, and the brake-controller and charge circuits. This is the core of the retrofit.
• Brake controller: a modern proportional controller wires into the truck; many GMT800s have a factory brake-controller connector under the dash that makes this plug-and-play. If yours doesn’t, it’s a wired-in install.
• Tow mirrors: swap to extendable/tow mirrors for visibility — options range from manual to powered/heated depending on what you want and your door wiring.
• Hitch/receiver: add or upgrade the receiver to match your trailer weight.
• Transmission cooler: a big one for towing — an aftermarket cooler helps keep the 4L60E/4L80E alive under load.

What you can’t just “add”

• Tow rating: your truck’s rating is set by its axle ratio, transmission, brakes, and build — bolting on a hitch doesn’t raise it. Know your real capacity.
• A stronger transmission: if you have a 4L60E and need 4L80E capability, that’s a swap, not a bolt-on.

Do it in the right order

 

1. Confirm what you have (RPO codes, existing connectors).
2. Add the trailer wiring and 7-pin.
3. Install the brake controller (check for the factory connector first).
4. Add tow mirrors and, if you tow often, a transmission cooler.

Common mistakes to avoid

• Assuming a hitch raises the tow rating. It doesn’t — respect the truck’s real capacity.
• Skipping the transmission cooler on a truck that tows regularly.
• Cheap trailer wiring taps that corrode and cause light gremlins — do it properly.
• Overlooking the factory brake-controller connector and hard-wiring unnecessarily.

FAQ

Does my truck have the brake-controller plug? Many GMT800s do, under the dash near the steering column — check before buying a hard-wire kit.

How do I find my tow rating? It depends on axle ratio and configuration — see the towing guide and confirm your RPO axle code.

Discuss it on the forum

Adding tow gear to your GMT800? Post your RPO codes and what you’re pulling in the FullSizeChevy GMT800 forum. For the receiver end of the job, the GMT800 hitch upgrade walkthrough shows a factory-to-heavy-duty swap, including the weld-on 7-way bracket. Related: Silverado towing guide and GM rear axle RPO codes. See the GMT800 hub for the full platform overview — every model, engine and repair guide in one place.

Find every repair, buying, maintenance, and troubleshooting guide in the GMT800 Owner’s Hub.