All Star Truck Parts 4-Headlight H4 Relay Wiring Harness — 4-Relay Kit with Ceramic Sockets for Brighter, Stable Halogen Output

An All Star Truck Parts 4-headlight H4 relay wiring harness replaces weak factory headlight circuits so your H4 bulbs get stable, full battery power via relays while still using the stock switch to activate them. Upgrading to brighter halogen bulbs or experiencing dim, flickering, or overheating headlights is often caused by the original headlight switch and wiring being unable to handle increased current. This relay harness routes power directly from the vehicle battery to each headlamp through four relays and ceramic H4 sockets, relieving the factory wiring and improving electrical reliability without altering dashboard operation.

How does this harness improve headlight brightness and consistency?

The harness supplies full battery voltage to each H4 headlamp through dedicated relays, avoiding voltage drop across the stock switch and thin wiring. That ensures bulbs run at their intended output for steadier illumination and fewer flicker events.

• Four relays provide direct battery feed to each headlight circuit.
• Ceramic H4 sockets resist heat, reducing plug failure.
• Maintains use of the factory headlight switch as a relay trigger.

Will this harness stop headlight overheating and switch overload?

Yes — by diverting the headlamp current away from the stock switch and wiring, the harness prevents the switch from carrying heavy loads that cause overheating and early wear. The ceramic sockets and heavier gauge wiring are designed to tolerate higher currents typical of upgraded bulbs.

• Heavier gauge power wires minimize heat buildup.
• Ceramic plugs reduce melting and contact deterioration.
• Relays handle switching instead of the dash switch contacts.

Is this harness compatible with my headlamp sizes and H4 bulbs?

The harness is built for vehicles using H4 plug-style headlamps and works with common headlight sizes like 7x6", 4x6", and 5-3/4" when those fixtures accept H4 bulbs. It adapts to the bulb socket, so it’s ideal when factory sockets don’t reliably power upgraded halogen units.

• Designed specifically for H4 plug headlamps.
• Works with 7x6", 4x6", 5-3/4" and other H4-compatible fixtures.
• Plugs into existing harness locations for a clean install.

How difficult is installation and what does it include?

Installation is straightforward for anyone comfortable with basic vehicle electrical work: mount relays, connect the fused battery lead, and plug the ceramic H4 sockets into the headlamps and factory harness. Instructions and standard connectors are included so you avoid splicing stock wiring when possible.

• Includes four relays, fused battery lead, and four ceramic H4 sockets.
• Plugs to existing headlight connectors to reduce cutting or splicing.
• Mounting points and wiring lengths sized for most trucks and cars.

Who is this for? This All Star Truck Parts 4-headlight relay wiring harness is intended for drivers upgrading to higher-output H4 bulbs, repairing dim or flickering headlights, or replacing failing headlight sockets and switches. It suits DIY mechanics and professional installers who want a reliable, heat-resistant wiring solution that restores proper voltage to each headlamp while preserving dashboard control and vehicle aesthetics.

FAQ

Q: Will this harness work with my H4 halogen upgrade?

A: Yes. It’s designed for H4 plug-style bulbs and supports common sizes like 7x6", 4x6", and 5-3/4" when the fixture accepts H4 sockets.

Q: Do I need to alter the dashboard switch to use it?

A: No. The harness uses the stock headlight switch only to trigger relays; no dash switch modification is required.