How to Fix the Trucks Lighting System

Well, lights are fine when they’re working but when they fail and the system has been patched or added to, it can be a hair-pulling experience. Some systems have taken days to correct because of the extensive wiring of today’s trucks.

A lighting system is a machine of its own, with the battery being the heart of the system. First, look at the battery surface and the connections, if corrosion is visible, remove the cables and clean the posts and cables, check to see that the batteries are at least 12 volts and then load test them, replace if needed, then connect the cables and tighten.

The ground is the next most important thing to check out if you’re working on a trailer, pull the 7-wire plug and spread the tongs, the ground is the fat one on the top. If the lights were flickering or blinking with the turn signals, the ground is a good place to start, most of the time the wires pull out inside of the plug where they are screwed to the plug.

If you lost a section of lights and still have another section working, you may have a broken wire and if a circuit breaker is tripped from the lost circuit, a wire has rubbed through somewhere.

Corrosion on plugs and terminals often causes a loss of contact, everyone has there own sure-fire way of doing electrical connections so they won’t corrode, but they all do eventually, all you can do is slow the process by sealing the connections the best you can, grease is number one practice in use.

Light’s aren’t complicated, they just take time to track the problem. Most of the time there’s no power, so tracking the source of the problem can take a while.

Here’s a reminder of color codes for 7 wire systems used on trucks: White/ground | Black/marker & clearance | Yellow/left turn | Red/stop | Green/right turn | Brown/tail lights | Blue/aux power or ABS :: If replacing a light cord and the trailer has ABS, make sure you get an ABS coil cord to replace it. ::

There are many variables with light troubleshooting but if you start with the source and work your way to the accessory, you should find the problem attacking the system.(some reverse the procedure)