How to test trailer lights with a multimeter.

Properly functioning trailer lights are very important because if you’re on the road without them, you’d be risking your life along with other’s lives. They are especially important during the colder season when fog is all you see. However, no matter how much you care for them, they often stop working.

Before taking your multimeter out, you need to make sure that the problem is with the connections and not something else. How do you ensure that? Try replacing your light bulbs because the problem might lie with that and not with your trailer lights.

If it still does not work, then there might be something wrong with the wiring. To check this, remove the wires that connect the main vehicle to the trailer and then connect the lights directly to the trailer. If still, the lights do not operate, then you’ll have to take your multimeter out.

Checking for improper grounding

Usually, the problem lies with the grounding. To test your trailer lights’ grounding system, follow these steps:

  • Disconnect your trailer plugs
  • Set your multimeter to measure resistance (ohms)
  • Connect the black probe to the negative connection of the plug and the red one to the grounding. If the multimeter reads 0.3 ohms, your trailer lights are properly grounded.

Testing for voltage

If you haven’t already diagnosed a problem, the next step is to test for voltage.

  1. Examine your connector to know which wires are for which light. Usually, there are four wires, each with a distinct color with white for grounding.
  2. To measure the voltage, set the multimeter to the voltage setting. Make sure that you’re setting it to measure DC and AC. DC is represented with a straight line.
  3. Now, connect the black probe to the negative terminal and the red probe to one of the pins for the lights. Then turn the light on.
  4. Note the reading. Your multimeter should display the value in keeping with the voltage of the battery you use. So, if it’s a 12 Volt battery, the reading should indicate 12 Volts.

Testing the Wiring system

To test the lighting connector, you will have to measure resistance. To do so, follow the steps given below:

  1. Set the multimeter to measure resistance (ohms)
  2. Connect the leads to the multimeter.
  3. Now connect the red probe on each point pin and the black probe to the ground connection.
  4. Note the reading. If the reading is 3 ohms, your wiring system is fine.
  5. However, for the wires that control two or more functions, you will have to test each bulb individually because since they’re connected in a series connection, the reading you see is the least. By testing each bulb separately, you will be able to identify exactly where the problem lies.