How to Troubleshoot a Trailer Light

There's a light out on your trailer, but how do you know if it's just a bulb, or something more serious? Perhaps you have already replaced the bulb but the light still doesn't work. You can find and fix the problem with a test light and a little bit of work.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• 12-volt test light Solderless connectors Electrical tape Sandpaper

1. Check the trailer connector for damaged pins. Replace by splicing in a new connector if damaged pins are found.

2. Examine the overall condition of the trailer wiring. If the general condition of the wires is poor, replacement of all the wires is suggested.

3. If the taillights work, but go out when the vehicle brakes are applied, check the connection of the white ground wire to the trailer frame. A bad connection here will cause this problem, and is the likely culprit when the trailer lights blink on bumps in the road. To repair, remove and replace the screw holding this terminal to the trailer frame, being sure to remove any rust at the contact point.

4. Isolate the problem circuit and look for obvious breaks in the wires. If, for example, the right-side marker light is out but all the taillights and other marker lights work, check for a break in the connection at the problem light.

5. Remove the bulb and use a test light to check for power at the lamp's center terminal if no wire breaks are found. Power here would indicate either a bad bulb or a poor ground at that lamp. If another bulb doesn't cure the problem, remove the lamp from the trailer and clean the ground connection, both on the lamp and the area of the trailer where contact is made.

6. Check for areas where the insulation has been rubbed off the wires if the trailer blows vehicle fuses. Replace any damaged section of wire by spicing in a new piece using solderless butt connectors.