Troubleshooting Trailer Running Lights Circuit Not Functioning on Fifth Wheel

Question

Question:

fifthwheel no running lights,have turn signals and brake light, trailer fuses are good.

asked by: Joe

0

Expert Reply:

First thing you should do at this point is test the 7-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.

If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the problem is on the vehicle side then I would first recommend you double check how the harness is installed on your vehicle, make sure all of the connections are good and tight. You should check all towing related fuses and relays as well.

expert reply by: Jameson C

0

click to enlarge

Answer 1

I absolutely agree with you that what you are experiencing is a ground issue; moving it to a frame with a clean metal surface is going to resolve the issue in nearly every case. If it was a short you would still be having issues with lights not…

view full answer...

Answer 2

If you are not getting power on the running light circuit at the connector on the truck then none of the running lights should be working on the trailer. Trailer's in the US use one circuit for running lights, one circuit for left turn/brake…

view full answer...

Answer 3

Everything works okay until you activate the running lights and draw maximum amperage through the system. This is the classic symptom of an insufficient ground connection. Find the main grounding point on the trailer by tracing the white wire from…

view full answer...

Answer 4

It sounds like there is a ground wire issue on your trailer. Since you said you checked the vehicle harness, and it checks out we can rule that out as the issue. You will want to use a circuit tester like part #PTW2993 and check the wires coming out…

view full answer...

Answer 5

My suspicion is that you have a poor ground connection somewhere on your trailer. The fact that everything works fine until the running lights are turned on is the dead giveaway. When the tail lights are turned on, the trailer lighting is drawing…

view full answer...

Answer 6

First thing to check is for corrosion on the trailer wiring connectors on the running light circuit. Nearly everytime a single circuit stops working on trailer wiring it's due to corrosion in the connectors preventing the connection being made.…

view full answer...

Answer 7

Since all of your trailer lights operate properly with the exception of one of the running lights, this tells us that the vehicle wiring harness is probably working properly. I would first carefully check the bad light's ground and power wires to…

view full answer...

Answer 8

LED lights only require a very small amount of amperage/voltage to partially light up. What you are experiencing is a little bleed through on your running light circuit. So somehow there is a small short between an active circuit on your trailer…

view full answer...

Answer 9

This sounds like a ground issue. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light. Make sure that the vehicle side and…

view full answer...

Answer 10

You will first want to check the fuses on your tow vehicle. Some vehicles could have fuses for operating the turn signals and brake lights of a towing package. You will want to check if they are installed and working properly. The next thing is to…

view full answer...

Answer 11

The difference between the Class II and Class III hitches has to do with their Gross Trailer Weight (GTW), their Tongue Weight (TW), and their Hitch Receiver Size. Class II trailer hitch receivers have a 1-1/4 inch receiver and can be rated up to…

view full answer...

Answer 12

A 4-Way trailer connector has the basic lighting functions only; running lights, left turn signal and brake lights, right turn signal and brake lights, and ground. A 7-Way has these functions and a 12 volt circuit, a circuit for electric trailer…

view full answer...

Troubleshooting Trailer Running Lights Circuit Not Functioning on Fifth Wheel

Products Featured in This Question

Featured Help Information

Miscellaneous Media

Continue Researching