How to Check Trailer Lights and Wiring Yourself (Safely)

A trailer light problem doesn't always need a mechanic's visit to at least narrow down — a few basic checks, done safely with the trailer parked and unhooked from traffic, can save time on the phone and help the eventual repair go faster.

Start at the connector

With the trailer parked safely, unplug the electrical connector and look for corrosion, bent or pushed-in pins, or debris inside the plug. A quick visual check here catches a surprising number of lighting issues before you even get to the wiring itself.

Test each function one at a time

Have someone apply brakes, turn signals, and running lights one at a time while you watch each light. Note exactly which lights work and which don't for each function — "the left brake light doesn't work but the left turn signal does" is far more useful than "the lights are broken."

Wiggle-test the harness (gently)

With the trailer's lights on, gently flex the harness near the connector and along any visible sections to see if a light flickers — that's a strong sign of a chafe point or loose connection at that spot. Don't pull or force anything; you're just looking for a reaction, not trying to fix it yourself.

Bring what you found to the call

Whatever you find — corrosion, a specific light that's out, a spot where wiggling the harness causes a flicker — tell #1 Taz exactly that when you call. It turns a generic "my lights don't work" repair into a targeted fix, whether that happens mobile or at the Cottonwood shop.