Connect your vehicles headlight bulbs to FULL BATTERY VOLTAGE for MAXIMUM BRIGHTNESS! At Aspire Auto Accessories, we manufacture and carry our own Heavy Duty Relay Harnesses that fit a wide selection of bulbs commonly found in most vehicles. This kit is designed to fit vehicles originally equipped with 9004 (HB1) bulbs and CONVERTED to 9007 (HB5) bulbs. 


For harnesses designed to fit non-converted vehicles equipped with either 9004 (HB1) OR 9007 (HB5) bulbs:


Build your harness: Select your options


Step 1: Select Wiring Harness Gauge

  • 14 Gauge (Included) - Our standard wire gauge
  • 12 Gauge (+$20.00) - Upgrade your wires that goes to the harnesses plugs and factory harness to thicker wire.


Step 2: Select Power Wire Gauge

  • 14 Gauge (Included) - Our standard wire gauge
  • 12 Gauge (+$8.00) - Upgrade your power wire that goes to the harnesses relays and your vehicle's battery to thicker wire.


Step 3: Soldered Connections

  • No (Included)
  • Yes (+$7.00) - Have us solder your machine crimped connections so you can have the most secure & reliable harness. Solder is NOT common in vehicles, but is routine in aircraft because it produces the best union of wire to terminal.


Additional Information: Connector Type

  • High Temperature Connectors with Moisture Seals (Included) - Maximum Temperature = 572º F / 300º C 


All connections are machine crimped and shrink wrapped to the highest industrial standards.


Why use a Heavy Duty Relay and Headlight Wiring Harness Upgrade?


Reason #1: To minimize the VOLTAGE DROP in factory headlight systems. Voltage drop lowers the energy delivered to your headlight filaments which reduces their output. Voltage drop is a result of electrical power being run for long distances through thin wires. You can visualize voltage drop by imagining yourself drinking a beverage through a long thin straw (electric energy is the "beverage" and the wire is the "straw").


Reason #2: Using a 9004 (HB1) to 9007 (HB5) Heavy Duty Relay and Wiring Harness Upgrade reduces the current that is handled by the head light switch by a large margin. This reduction in current greatly increases the life of your head light switch.


For example: Your factory headlight systems POWER flows from BATTERY to HEAD LIGHT SWITCH in passenger compartment. When head light switch is turned on, POWER flows back out into engine compartment and then illuminates HEAD LIGHTS. Notice the long distance that power must travel. To make matters worse, typical factory headlight wires are 18 Gauge or LESS. These long runs of thin wires starve your head lights of energy.




Increases the power delivered to your head lights by minimizing the distance power must flow from battery to head lights AND by passing this power through thick, 14 Gauge or 12 Gauge USA made wire (Smaller Gauge = THICKER wire) with the highest quality copper conductor. 




POWER flows from BATTERY to HEAD LIGHT SWITCH in passenger compartment. When head light switch is turned on, POWER flows back out into engine compartment and then ACTIVATES RELAYS on the wiring harness. The RELAYS then CONNECT the HEAD LIGHTS DIRECTLY to BATTERY through 14 Gauge or 12 Gauge wires.


In simplified terms, the 9004 (HB1) to 9007 (HB5) Heavy Duty Relay & Headlight Wiring Harness Upgrade is triggered by the head light switch and when triggered, the harness supplies power to the head lights through a more efficient path.


This relay and wiring harness upgrade is one of the most simple and effective ways to improve dim headlights and overall headlight performance by increasing both your low beam and high beam illumination. Perfect for dark roads, off-road, and rural areas! 


PLEASE NOTE: Daytime Running Lights (DRL) that utilize the low beam or high beam headlamps at a reduced intensity for illumination must be disabled in order to use this harness.


Can't find a harness that fit's your vehicle's bulbs or unsure about product fitment? If you have any questions, please let us know and we'll be happy to help! 


🎁 Free Dash and Steering Wheel Wipe + Free Brite Box Sticker with every purchase! 


Tip: When selecting your options, go in order step 1 thru 3 for the best results.

9004 - 9007 Heavy Duty Headlight Relay Harness

PriceFrom $79.99
Excluding Sales Tax
Step 1: Wiring Harness Gauge
Step 2: Fuse Holder & Power Wire Gauge
Step 3: Soldered Terminals
  • • Smart & Heavy Duty harnesses are MADE IN THE USA!

    • 100% Plug and Play Installation. 

    • 14 Gauge Headlight Wires - Our wire is USA made. Don't settle for import wire! Import wire typically has extra thick insulation that makes the copper "under gauge"! Additionally, most import wire we see has very poor quality copper.

    • 30 / 40 Amp Relays.

    • Control Module is fully encapsulated for waterproofing and vibration resistance. (Smart Harness)

    • Wires are encased in split loom tubing for protection.

    • Fuse Protected with water resistant fuse holders.

    • One Year Warranty