A good quality 12-volt test light (from Snap-On or Matco), or a Multimeter can often be your best friend that deserves a special place in your tool box! Get one!!!

If you turn the lights on & find a clearance light that is out, first remove it from its mounting position & check for power. Connect the ground clip on the test light to the terminal post on the connector that has a WHITE wire going into it. Use the probe end to check for power on the post with the black (marker light circuit), red (turn signals, or brake lights circuit) or brown wire (tail light circuit) going into it.

If the test light or meter indicate voltage, then the light itself is bad.

If they DON'T indicate voltage, then take the ground clip & find a bare metal spot to hook it up to. If the light works when you touch the probe to the POSITIVE side post, then you have narrowed the problem to a bad ground circuit. Trace the white wire from the connector to its ground point. Dirty & corroded ground points will cause a lot of problems!

On trailers, all too often an entire circuit of lights will decide to go out at once. Most commonly the problem is in the light cord socket/ breaker box on the nose of the trailer & the prongs in the socket just need to be spread apart with a pocket knife or similar object, taking care not to spread 'em open too far.

A corroded power supply connection. If the connector & light have corrosion on the terminals, then both need to be replaced.

By Jeff Barker

Co-Adminstrator and Editor
TruckstopUSA.com

*Note: This article is for information purposes only. Neither the author or the owner of this website assume any liability for, or arising from the content of this article.