Wiring a few rock lights is simple. Wiring 8–12 lights around an entire truck is where harness design starts to matter.
Long wire runs, cumulative amperage, voltage drop, fuse sizing, connections, and where power enters the harness can all affect performance.
Here are the basics we consider when designing Shadow Eliminator™ harnesses—and what you should know if you're building your own.
Note: This is general educational information. Wire sizing and circuit protection can vary based on wire type, circuit length, temperature, routing, connectors, and the components being used.
Start With Current Draw
The lights used in our current Shadow Eliminator systems draw approximately:
XL Light — 1.6A each
Magnetic Light — 0.5A each
That gives us:
CORE — 8 XL Lights
8 × 1.6A = 12.8A
MAX — 8 XL + 4 Magnetic Lights
12.8A + 2A = 14.8A
That means a MAX harness needs to distribute roughly 15 amps across the vehicle.
That's why simply connecting everything to one long piece of small wire isn't ideal.
What Gauge Wire Should You Use?
Wire size depends on both current and distance.
A wire may technically carry the required amperage, but over a long run its resistance can create excessive voltage drop.
General 12V Automotive Wiring Guide
This is a general starting point for quality copper automotive wire, not a universal specification.
We also recommend avoiding cheap copper-clad aluminum (CCA) wire for this type of installation. Quality copper automotive wire provides better conductivity for a given gauge.
Use a Larger Main Trunk and Smaller Branches
One of the better ways to build a multi-light harness is to use a larger main trunk with smaller wires branching off to each light.
Think:
Power → Main Trunk → Individual Light Branches
The main wire carries the combined load of several lights, while each individual branch only carries the current required by that light.
For lights with similar current draw to ours, a practical starting point is:
XL light (~1.6A): typically 18 AWG branch wire
Mag light (~0.5A): approximately 18–22 AWG depending on branch length and installation
The important part is that 18–22 AWG branch wire should not automatically be used as the main feed.
A branch may only carry 0.5–1.6A.
The beginning of the main harness could be carrying 12–15A.
Be Careful With Long Daisy Chains
Imagine eight 1.6A lights running along one long harness.
The beginning of the circuit may be carrying:
8 × 1.6A = 12.8A
As each light branches off, the current carried by the remaining trunk decreases.
If the beginning of that harness is too small, you can end up with:
- Voltage drop
- Dimmer lights toward the end
- Heat at wires or connections
- Unnecessary electrical losses
This is why harness architecture matters just as much as individual wire size.
Where Should Power Enter the Harness?
Don't automatically feed a long perimeter harness from one extreme end simply because that's where the battery is.
For a large vehicle, it can sometimes make more sense to split the harness into multiple major branches.
For example:
POWER
↙ ↘
Driver Side Passenger Side
Another option is feeding closer to the electrical center of the harness so current travels shorter distances in multiple directions.
The best configuration depends on the vehicle, battery location, light count and harness routing.
The goal is simple: Reduce unnecessary distance while distributing the load efficiently.
Watch Your Voltage Drop
Voltage drop increases with current, resistance and wire length.
The easiest way to check your finished harness is to turn every light on and measure voltage:
At the power source
vs.
At the furthest light
Testing under load matters. A harness can pass a continuity test and still perform poorly when 15 amps are actually flowing through it.
Fuse the Harness Properly
Your fuse doesn't just protect the lights—it primarily protects the wiring.
The main fuse should generally be installed as close to the power source as practical so that the main feed is protected if it shorts against the vehicle.
Fuse sizing should account for both:
Normal system current AND the safe capacity of the wiring/components being protected.
For higher-current lighting systems, it's also often better to use the dash switch or switch panel to trigger an appropriately rated relay rather than routing the entire lighting load through a small switch.
Connections and Routing Matter Too
Even oversized wire won't save a poorly assembled harness.
Use quality:
Automotive copper wire • sealed connectors • properly crimped terminals • abrasion-resistant loom • heat shrink/sealed splices where appropriate
Keep the harness away from:
Exhaust • sharp edges • driveshafts • steering • suspension • tire-contact areas
And secure it so it can't constantly move or rub against the chassis.
Magnetic Zip-Tie Mounts Make DIY Harnesses Easier
If you're building your own harness, ADV Magnetic Zip-Tie Mounts are one of our favorite ways to route wiring cleanly.
Anywhere there's a suitable steel surface, they give you a repositionable mounting point for:
Wiring harnesses • air lines • accessory wiring • camper wiring • temporary trail repairs
They're especially useful while building a harness because you can reposition the wiring several times before deciding on the final route—without immediately drilling additional holes.
For critical areas where movement or loss of a magnetic mount could create a hazard, use an appropriate mechanically secured mounting method instead.
Test Before You Call It Finished
Once everything works, leave the complete system running for 15–30 minutes.
Check:
Voltage at the furthest lights
Main wiring for abnormal heat
Splices and connectors for heat
Fuse holder and relay
Brightness consistency
Harness routing and abrasion points
Then inspect it again after the vehicle has actually been driven.
Off-road wiring needs to survive more than a garage test.
Building Your Own vs. Plug & Play
Shadow Eliminator™ is available with a DIY wiring option for customers who prefer to build their own electrical system or add additional lights.
For customers who don't want to calculate wire lengths, branch locations, connectors, power distribution and vehicle-specific routing, we also offer an ADV Plug & Play Harness.
Either way, the same principle applies: A good harness isn't just about getting power to the lights. It's about getting the right amount of power to every light efficiently, reliably and safely.
Shadow Eliminator™ — Full-perimeter lighting engineered specifically for your vehicle.