The Diode Dynamics Add-On Fog Light Wiring Harness lets you add fog lights to a vehicle that didn't come with them from the factory. Once installed, the fog lights function just like OEM — they turn on automatically with the headlights when the fog light switch is in the on position. Two wiring methods are available depending on whether you're adding a new switch or using an existing OEM upfitter/auxiliary switch. Here's the full walkthrough.
Table of Contents
- Tools Required
- Method One — Add New Switch to Vehicle
- Method Two — Use OEM Upfitter/Auxiliary Switch
- Functional Notes
- Fog Light Aiming Instructions
- Questions About the Install?
- Shop Fog Light Harnesses at Ess K Customs
Important: When routing harnesses, avoid areas subject to heat buildup or moving parts. Follow the path of the original manufacturer's wiring harnesses wherever possible.
Tools Required
- Basic wiring tools
Method One — Add New Switch to Vehicle
Step 1 — Route the Wiring Harness
Route the wiring harness near the fuse box under your hood. Run the output wire to the fog light location on each side of the vehicle. Route the switch wire into the vehicle cabin on the driver's side.
Step 2 — Connect Battery Leads
Connect the positive (VB) and negative (G) battery wires to the battery, or to the main power terminals near the fuse box.
Step 3 — Connect the Activation Wire
Connect the Activation Input Wire (DW) to your preferred activation signal (AW). When this signal is powered and the switch is on, the fog lights will turn on. We recommend tapping the sidemarker or low beam signal so the fog lights turn on and off automatically with your parking lights or low beams.
Step 4 — Connect the Deactivation Wire
Connect the Deactivation Wire to your preferred signal to disable the fog lights when 12V is applied. We recommend tapping the high beam signal so the fogs switch off when high beams are activated.
Step 5 — Connect the Backlight Wire (if applicable)
If you purchased a 4-pin harness with a backlight wire, connect the Backlight Activation Wire (BW) to a fused 12V source to trigger the backlight feature. Check local laws and regulations for on-road use of the backlight feature.
Step 6 — Wire the Switch
Connect the Switch Input Wire to the Fog Relay (S). Inside the cabin, connect the switch wires to the switch, aligning wire colors as shown in the included diagram. Provide ground to the fog light switch using the included grounding wire (SG). Mount the switch in an unused area of the dash.
Step 7 — Connect Output Wires and Test
Connect the output wires to the fog light on each side of the vehicle. Secure all wiring and test for function.
Method Two — Use OEM Upfitter/Auxiliary Switch
Step 1 — Route the Wiring Harness
Route all wires following the same instructions as Method One, but do NOT run switch wires into the vehicle cabin.
Step 2 — Replace the Power Input Wire
Unplug the Battery Input Wire (VB) from the Fog Relay and replace it with the Power Input Wire (VS). Using a standard crimp tool, connect the Power Input Wire (VS) to an OEM Auxiliary Switch wire on your vehicle. Ensure the wire can provide adequate current — reference your vehicle manual.
Step 3 — Connect Activation, Deactivation, and Backlight Wires
Connect the Activation Input Wire (S) to your parking light or headlamp circuit. Connect the Deactivation Wire to your high beam signal. If equipped, connect the Backlight Activation Wire (BW) to a fused 12V source. Your fog lights will now activate any time the activation circuit is powered and your upfitter switch is in the on position.
Step 4 — Connect Output Wires and Test
Connect the output wires to the fog light on each side. Secure all wiring and test for function.
Functional Notes
- The activation wire should be connected to an appropriate signal — do not connect to constant 12V power or ignition power, as this would allow the fogs to be switched on at any time.
- The deactivation wire disables the fog lights when 12V is applied.
- Any backlight feature is intended as accent illumination only. Check local laws before using on public roads.
Fog Light Aiming Instructions
Step 1 — Park 25 feet from a wall on a level surface.
Step 2 — Measure the distance from the ground to the center of the fog light (mounting height).
Step 3 — Mark the mounting height on the wall with tape.
Step 4 — Add a second tape mark four inches below (fog light cutoff line).
Step 5 — Aim each fog light so the top of the beam pattern aligns with the cutoff line. The install is complete.
Questions About the Install?
If you run into any issues during the installation, contact Ess K Customs — as an authorized Diode Dynamics dealer, we're here to help.
Shop Fog Light Harnesses at Ess K Customs
Ready to add fog lights to your ride? As an authorized Diode Dynamics dealer, Ess K Customs carries genuine add-on fog light wiring harnesses with full manufacturer warranty.
Browse Add-On Fog Light Harnesses at Ess K Customs →
This install guide applies to Diode Dynamics SKUs: DD4109, DD4110, DD4111, DD4112, DD4113