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Possible Causes for Dim Trailer Lights


My trailer lights work but they are weak...what could be the problem?


Expert Reply:

Most often the root cause for issues with trailer lighting is a weak ground. Strange as it may sound, a loose or rusty/corroded ground can cause a vehicle's trailer wiring harness to badly misbehave and shut down some functions. It may also just limit the amount of current that can flow to the lights and this will result in dim illumination.

The easiest way to check the trailer ground is to disconnect it from the vehicle and apply 12V power (from a well-charged 12V battery) directly to the trailer connector. You can use your vehicle battery or a spare. Apply the negative terminal to the connector ground and then one by one apply the positive terminal to the pins for the various light circuits.

If you find the lights are still dim even when directly powered from the battery then this tells you to focus on the trailer's wiring. Find the main ground wire for the trailer's wiring harness, usually a white wire, and check its connection to the trailer frame. The ground wire's ring terminal should be tightly secured to a clean bare metal surface. You can sand off that spot if corroded and/or clean it with a solvent to remove any grease, oil, dirt or other contaminants. Sanding off the primer/paint from that grounding point also helps. When you make the new ground connection apply dielectric grease # 11755 to protect that new clean connection.

On the vehicle if you have a multi-meter like # PT89ZR you can test the voltage on the trailer connector. If you read much less than 12 volts then check the ground for the vehicle wiring harness in the same way.

If you still would like brighter light output even after you address any grounding issues you may be able to substitute super-high-efficiency LED type bulb replacements for the standard incandescent bulbs. LEDs use about one-tenth the power required by typical bulbs and so they provide generally provide much brighter light. The linked page shows you all LED equivalents to the most popular bulbs. Just match up the your bulb number, such as a 194, which is quite popular. For this bulb we offer many LED alternatives.

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