How to Install Cab Lights on a Semi Truck (Step-by-Step Guide)
What Are Cab Lights?
Cab lights (also called marker lights, clearance lights, or roof lights) are the row of amber lights mounted on top of the cab. Federal regulations require trucks over 80 inches wide to have cab-mounted clearance lights — but that doesn't mean you're stuck with the dim, yellowed factory units.
Upgrading to LED cab lights gives you brighter illumination, lower power draw, and a dramatically sharper look — especially at night.
Choosing the Right Cab Lights
LED vs. Incandescent
LED cab lights last 50,000+ hours compared to 1,000–2,000 hours for incandescent bulbs. They draw less power, run cooler, and produce a cleaner, more consistent light. The price difference is minimal, so there's no reason to go with incandescent on a new install.
Amber vs. Clear Lens
DOT regulations require cab clearance lights to emit amber light. You can achieve this with either an amber lens over a white LED or a clear lens with an amber LED bulb inside. Clear lenses with amber LEDs give a more modern, clean look when the lights are off.
Smoke Lens Option
Smoked lenses are a popular choice for trucks with a dark exterior. The lens appears tinted when off but still emits bright amber light when on. Check your state regulations — some states require the lens itself to be amber colored.
Installation Steps
Tools Needed
- Drill with step bit (if installing new lights on a bare roof)
- Wire strippers and crimpers
- Butyl rubber sealant or silicone
- Phillips and flathead screwdrivers
- Multimeter for testing connections
Step 1: Remove Old Lights (If Replacing)
Disconnect the battery. Remove the lens or housing screws from inside the cab or from the exterior mounting screws. Unplug the wiring connector. Clean the mounting surface and remove any old sealant.
Step 2: Prepare the Mounting Surface
Apply a ring of butyl rubber sealant around the base of each new light before mounting. This is critical — roof leaks from cab light installations are the number one complaint, and they're 100% preventable with proper sealant.
Step 3: Mount the New Lights
Position each light on the roof, press firmly into the sealant, and secure with the mounting screws. Don't overtighten — you want the sealant to form a consistent gasket around the base.
Step 4: Wire the Connections
LED cab lights typically have two wires: power (positive) and ground (negative). If you're replacing existing lights, connect to the existing wires using weatherproof butt connectors or solder with heat shrink. If running new wiring, route the positive wire through the headliner to a switched power source and ground to the cab frame.
Step 5: Test and Seal
Reconnect the battery and test each light. Check for even brightness and correct color. Once confirmed working, apply a final bead of sealant around the base exterior for extra waterproofing.
Popular Models by Truck
- Kenworth T680 / T880: 5-light setup, oval lens shape. Shop T680 cab lights
- Peterbilt 389 / 579: 5-light setup, rectangular or torpedo style. Shop Pete 389 cab lights
- Freightliner Cascadia: 5-light setup, integrated into roof cap. Shop Cascadia cab lights
Professional Installation
If you'd rather leave the wiring to the pros, our technicians at Adam's Chrome Shop in Dallas install cab lights daily. Walk-ins welcome — typical install time is 1–2 hours.