There are various types of utility trailers and tow vehicles, and these different types can have different connectors for the wiring that goes to the trailer. The wiring is used to transfer signals such as turn signals and brake lights to the utility trailer lights. When the tow vehicle's right turn signal comes on, so does the right turn signal on the utility vehicle. It's important from a safety standpoint to check the utility trailer lights often to ensure they are working properly, especially if the utility vehicle is used in off-road situations.
Watch the lights of the utility trailer while someone in the tow vehicle uses all of the lighting system functions. These include the left turn signal, the right turn signal, the brake lights and the taillights, which should come on when the towing vehicle's lights are turned on.
Note which function is not working properly. If none of the utility trailer lights are working, the problem will probably be with the main power at the connector to the trailer wiring harness.
Check the connector that connects the wiring from the tow vehicle to the wiring in the utility trailer. You can usually pop off the connector by using a screwdriver on the latching arm. Use a voltmeter to see if the voltage is present, typically 12 volts, at each pin when the tow vehicle's light function is used. For example, when the tow vehicle's right turn signal is on, there should be 12 volts at the right turn signal pin. If voltages are present, the problem lies with the utility trailer wiring.
Connect the ohmmeter probes to see if there is a break in the wire for the light function that is not working properly. For example, if the right turn signal is not working, check the wire from the pin for that function to the right turn signal light at the back of the trailer. The ohmmeter probes will not be long enough for this, so you'll have to connect a jumper wire from one of the probes to the light. If there is continuity, the problem is most likely the light bulb. If there is no continuity, the wire is broken.
Visually trace the wire in question to find the break.
