Semi-Truck Trailer Light or Marker Light Malfunction | UpFix

Why Aren’t My Trailer or Marker Lights Working?

If you’ve replaced bulbs, fuses, and connectors and the trailer lights still don’t work, the issue is likely inside the truck’s lighting logic circuit. Modern trucks use BCM or relay-based lighting modules that control trailer light signals electronically.

Common Issues

• Trailer running lights flicker or fail

• Brake lights or turn signals intermittent

• Marker lights won’t stay on

• No voltage output at trailer connector

How UpFix Fixes It

UpFix repairs the internal lighting control circuits, replacing burnt relays and transistors. Each repair includes testing with simulated trailer loads to confirm consistent voltage output.

Why It Matters

Electrical malfunctions in lighting systems can result in DOT violations and unsafe operation. Repairing the control module ensures reliable lighting and avoids unnecessary rewiring.

Supported Brands

Freightliner, Peterbilt, Kenworth, Volvo, Mack, International and others.

Get your truck back on the road and keep your costs low.
Send your part to UpFix for professional testing and repair.
We’ll restore it to like-new condition, save you up to 80% compared to buying new, and make it plug-and-play ready when returned.