Car accidents usually occur due to distractions like kids fighting in the back, pedestrians crossing, honking horns, etc. Therefore, third brake light wiring is essential to create an extra signal to warn the driver behind, preventing rear-end collisions.
You can install this light in your vehicle, trailer, or both because it serves the same purpose. Let’s look at how to wire third brake lights below. Read on to learn more!
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What Is a Third Brake Light?
Also known as a Center High Mount Stop Lamp (CHMSL), a 3rd brake light kit is an essential safety feature that the NHTSA requires all cars to have. The device traces its origins to a psychologist named John Veovodsky, who tested the first version in 1974.
This gadget was a tiny, inexpensive light mounted at the base of the rear windshield, in the middle of it. Veovodsky connected the light to the brake circuit, so it turned on when the driver pressed the brake pedal.
The installation formed a triangle of red lights that were more effective at warning the drivers behind to stop.
A third brake light
Veovodsky installed the light in 343 taxi cabs in San Francisco but left 160 with the regular two lights.
The experiment commenced with taxi dispatchers assigning drivers randomly to both cab types (those with three lights and those with two). After ten months, the results were in. The taxis with a third brake light had fewer rear-end collisions than those without the lights.
To be more specific, they had 60.6% fewer collisions. Plus, the taxi drivers of the cabs with the third brake light experienced 61.6% fewer injuries than the rest.
Collisions also require repairs, and the repair costs of the taxis without the brake light were 61.8% more.
A third brake light on a sedan
The NHTSA noted this data and informed car manufacturers to include this 3rd brake light fixture in all passenger vehicles in 1986. It later extended this requirement to light trucks in 1994.
Was The Requirement Effective?
The NHTSA followed up on its requirement by checking the crash data reported by the police in eight states and found a reduction of rear-end collisions by 4.3%.
These findings were less dramatic than what Veovodsky found during his experiment, but the numbers made sense. The number of injuries, deaths, and property damage from crashes reduced significantly.
Therefore, the lights have become standard, and modern cars feature LED third brake lights that are more visible than their incandescent counterparts.
A 3rd stop light (LED strip) on a modern car
Third Brake Light Wiring
If your vehicle does not have this light (older than 1986) or has a damaged light/wiring, follow these steps to get this component functional.
You will need the following tools and materials.
- 3rd brake light assembly
- Heat shrink tubing or electrical tape
- Wire stripper
- Crimping tool
- Solder gun and tools
- Butt connector
- Wires (red or black power wires and green ground wire)
Step 1: Determine the Installation Area
Cars or trailers without this light don’t have slots for mounting it. So first, determine the most suitable location for installing the gadget.
The general area should be in the middle and above the rear windshield or trunk lid. When you press the brake pedal, this light should create a triangle of red lights with the other two.
After getting the right spot, mount this light. There is the option of installing a spoiler with this light mounted on it, which can make your vehicle look better.
A 3rd stop light mounted on the bumper
Step 2: Access the Brake Light Circuit
These wires run inside the vehicle, so remove the interior trim panels near the brake lights to access them. But the wiring harness doesn’t connect to the brake lights alone. It powers the entire rear light assembly, so find the individual brake wire.
Tail light wiring
You can use a multimeter or test light to check which wire transmits the electric current when you press the brake pedal.
Usually, it is the red wire, but it can be another color that distinguishes it from the turn signal and reverse tail light wire.
Step 3: Prepare the Wires
Once you identify the brake wire, cut it while leaving a sizable length to the brake light (like a pigtail). Also, cut a length of wire that can reach the 3rd light pigtail from the location of the cut brake light wire. Strip the ends of these wires to expose the copper metal conductor.
A 3rd brake light with its pigtail
Step 4: Link the Wires
Connect the 3rd brake light power wire to the two cut wires and secure the joint using a butt connector or solder. You’ll need a crimping tool if using a butt connector, then heat the outer tube with a heat gun to shrink it.
If you solder the joint, install a heat shrink tube above it and heat it to insulate the metal conductors.
A 3rd stop light mounted on a SUV
Remember to ground the third brake light by connecting its negative wire to an unpainted metal surface on the car’s body. Mount it using a self-tapping screw and apply dielectric grease above this ground connection.
Step 5: Test the Lights
Press the brake pedal and ask someone to check if all three lights turn on. Alternatively, you can park your vehicle with the trunk facing a large reflective surface, such as building windows, to check the reflection.
Step 6: Attach/Secure the Wires
Before reassembling the panels and trims, attach the 3rd brake light wires to the vehicle and secure them using grommets and cable clips to prevent wear from friction with other components. The clips should keep them tight.
Cars lined up on an expressway with three brake lights (note the improved visibility)
Wrap Up
Most people assume third lights as regular brake lights. However, if not for Veovodsky, rear-end collisions would have been common on our roads, especially when driving at night or during rainy or foggy conditions.
Wiring these lights is relatively straightforward because you only have to tap into the brake light circuit.
You can learn more about how to wire the brake light switch here to get a holistic understanding of the electric part of the braking system.
Comment below if you need third brake lights or their wires to hook up this safety light to your vehicle.
