Trailer lights not working at all

Symptoms

• No trailer lights work, including running lights
• Lights worked before but stopped suddenly
• Connector plug looks corroded or loose

Likely causes

• CommonBad ground connection at the trailerTrailer lighting circuits rely heavily on a solid ground, and corrosion or a loose ground wire causes widespread light failure.
• CommonCorroded or damaged connector pinsThe plug connecting the tow vehicle to the trailer is exposed to weather and road grime, leading to corrosion over time.
• CommonBlown fuse on the tow vehicle's trailer light circuitMany vehicles have a dedicated fuse for trailer lights that can blow from a short.
• PossibleDamaged or pinched wiring harness along the trailer tongueWear from flexing or road debris can damage the harness where it's most exposed.

What to do

1. Check the tow vehicle's fuse box for a blown trailer light fuse and replace it if needed.
2. Inspect the connector plug on both the vehicle and trailer for corrosion, bent pins, or looseness, and clean or reseat as needed.
3. Check the trailer's ground connection, usually a wire bolted to the frame, for corrosion or looseness, and clean/tighten it.
4. Use a test light or multimeter at the connector to check for power on each pin (running lights, brake lights, turn signals) with the tow vehicle's lights on.
5. Inspect the wiring harness along the trailer tongue for visible damage, pinching, or exposed wire.
6. If power is present at the connector but lights still don't work, check individual bulb sockets and ground points at each light fixture on the trailer.

Tools and parts

• Test light or multimeter
• Wire brush
• Dielectric grease

When to call a pro

If wiring, ground, and connector all check out but lights remain dead, have a trailer or auto electrical shop trace the harness for a break.

Safety