HERCOO Light Module for GM Trucks — 2003–2007 Silverado/Sierra Relay Adapter, Enables Low/High/Fog/DRL Simultaneous

The HERCOO Light Module is a compact aftermarket circuit board that lets your low beams, high beams, fog lights and DRLs operate together when high beams are engaged, improving overall front illumination on compatible GMT800 and related GM trucks.

This little plug-and-play module was designed for older GM full-size trucks and SUVs to restore or modify their headlamp logic so multiple front lamps can be active simultaneously. Made from FR-4 PCB material, the unit installs in minutes by replacing four factory relays in the engine-bay fuse box. It’s a simple electrical adapter — not a bulb or lamp — that changes how the vehicle routes power to the headlight circuits.

How does this module change my truck’s lighting behavior?

When installed, the module allows low beams, high beams, fog lights and daytime running lamps to be powered at the same time while the high beams are on. When high beams are off, the low beams, fog lamps and DRLs work as they normally would. This modifies the factory wiring logic without cutting or splicing wires.

• Simultaneous operation of low, high, fog, and DRL when high beams are enabled
• Preserves normal function when high beams are not in use
• No permanent wiring changes; uses existing relay locations

Which vehicles is the HERCOO module compatible with?

The module fits a range of GM GMT800-era trucks and some related models from the mid-2000s. Confirm compatibility by checking year and model against your owner’s manual or by visually matching the relay cluster layout in your engine bay.

• Chevrolet Silverado 1500/2500/3500 (2003–2007 variants listed)
• GMC Sierra 1500/2500/3500 and Yukon/Yukon XL models from early–mid 2000s
• Cadillac Escalade (2004–2006), Avalanche, and select GMT800 trucks

What’s involved with installation and do I need special tools?

Installation is intentionally straightforward: locate the fuse/relay box, remove the four relays labeled Hdlp-Hi, Hdlp-Low, Fog Lp, and Drl, set the HERCOO board in place, and reinstall the relays. No cutting, soldering, or special tools are required, and the procedure typically takes under five minutes.

• Find the factory relay cluster in the engine compartment
• Remove and replace the specified relays with the board in place
• No modifications or extra wiring; reversible and service-friendly

Is the product durable and what does the package include?

The module is built on FR-4 PCB, a common, sturdy material for small automotive circuit boards. It’s designed to tolerate the under-hood environment when installed in the relay pocket and handled as intended. Packaging includes one HERCOO high-performance front-lamp control circuit board and customer support through the seller’s email for post-purchase questions.

• Constructed from FR-4 PCB for structural stability
• Includes one HERCOO light module in the package
• Seller offers email support for installation or compatibility concerns

Who is this for? The HERCOO Light Module suits owners of mid-2000s Chevrolet, GMC, and Cadillac trucks or SUVs who want stronger combined front-light output without rewiring. It’s ideal for hobbyists, DIY mechanics, and drivers who need wider visibility in low-visibility conditions and prefer a reversible, plug-and-play electrical solution rather than replacing lamps or modifying factory wiring.