Trailer lights out
Can I keep driving?
Check the brake lights and turn signals before you move. If they work and it is daylight, finish the leg and book a bay. If they do not, or it is dark, get a mobile tech to the trailer.
Do this first
- Start at the plug. Pull the seven-pin, look for green corrosion, bent or pushed-back pins, and a cord that has been dragged. Clean the pins, plug it back in firmly, and try the lights again. This fixes more trailer light complaints than any part.
- Sort out what is dead. All lights dead points at the plug, the main ground, or a blown fuse or breaker on the tractor side. Only one circuit dead, for example all markers or one turn signal, points at that circuit's wire or its ground. One lamp dead is a lamp or its pigtail.
- Try another trailer or another tractor if one is nearby. Swapping tells you in a minute which side owns the problem, and the shop will ask the same question when you call.
What it usually costs and how long it takes
Trailer electrical is cheap in parts and expensive in hunting:
- Plug, socket or pigtail. Common, cheap, and a roadside job.
- Ground. The trailer's main ground and the individual lamp grounds corrode at the frame. Cleaning or moving a ground is minutes; finding which one is the time.
- Chafed harness. A wire rubbed through at a crossmember or a slider rail. Repairable on the spot if the tech finds it, which on an older trailer with a lot of previous patches can take a while.
- Nose box or junction box. The most involved repair, and the one that usually means a bay.
Sealed LED lamps fail less often than incandescent, but when they fail they are replaced, not repaired.
Where to get it fixed
Cities with the most shops listing trailer and electrical work:
Frequently Asked Questions
Which lights do I actually need to be legal?
Federal equipment rules require working tail lamps, stop lamps, turn signals, license plate lamp, clearance and side marker lamps, and reflectors on a trailer, and all required lamps must work whenever the vehicle is operated. An inspector counts every one. At night, missing markers or tail lamps are a stop.
The lights work when I wiggle the plug.
Then it is the plug, the socket on the tractor, or the pigtail. Replace the worn part rather than living with the wiggle; the next time it drops out will be at night on a two-lane.
The markers work but the brake lights do not.
Different circuit, probably the stop-lamp wire or the stop-lamp switch on the tractor. Try the tractor on another trailer. If the tractor's own brake lights are also dead, the fault is on the tractor side.
Can I run with a lamp out if the rest work?
A single marker out is a defect at inspection, not usually an out-of-service, but a brake lamp or turn signal out is the kind of thing that gets you stopped. Carry spare lamps and a pigtail; a sealed LED swap is a five-minute job.
The lights flicker when I hit a bump.
A loose ground or a chafed wire making and breaking contact. It will go from flicker to dead. Mark where on the trailer it seems to come from and have it chased.
Does a trailer ABS light count as a light problem?
Different system, same plug. The ABS power and the lights share the seven-pin, so a bad plug can take both out. If the trailer ABS lamp is also on, say so; it points the tech at the plug and the ground first.
- Which lights do I actually need to be legal?
- Federal equipment rules require working tail lamps, stop lamps, turn signals, license plate lamp, clearance and side marker lamps, and reflectors on a trailer, and all required lamps must work whenever the vehicle is operated. An inspector counts every one. At night, missing markers or tail lamps are a stop.
- The lights work when I wiggle the plug.
- Then it is the plug, the socket on the tractor, or the pigtail. Replace the worn part rather than living with the wiggle; the next time it drops out will be at night on a two-lane.
- The markers work but the brake lights do not.
- Different circuit, probably the stop-lamp wire or the stop-lamp switch on the tractor. Try the tractor on another trailer. If the tractor's own brake lights are also dead, the fault is on the tractor side.
- Can I run with a lamp out if the rest work?
- A single marker out is a defect at inspection, not usually an out-of-service, but a brake lamp or turn signal out is the kind of thing that gets you stopped. Carry spare lamps and a pigtail; a sealed LED swap is a five-minute job.
- The lights flicker when I hit a bump.
- A loose ground or a chafed wire making and breaking contact. It will go from flicker to dead. Mark where on the trailer it seems to come from and have it chased.
- Does a trailer ABS light count as a light problem?
- Different system, same plug. The ABS power and the lights share the seven-pin, so a bad plug can take both out. If the trailer ABS lamp is also on, say so; it points the tech at the plug and the ground first.
This page is general guidance for professional drivers and is not a diagnosis of your trailer. Lighting requirements are set by federal and state rules and enforced at roadside; check the current rules for your route. Shop listings are provided by Trucker Path users and the businesses themselves; availability and pricing are confirmed by the shop, not by Trucker Path.