Troubleshooting Lighting Functions on Trailer Wiring Harness on 2004 Dodge Ram 1500

Question

Question:

just put on a new pigtail on the truck. brake lights and turn signals work, but the running lights dont work and with the headlights on the taillights work on the truck but not on the trailer. also did not work on a different trailer. 2004 Dodge 1500 standard cab

asked by: Stephen

0

Expert Reply:

The lighting malfunctions you describe could be caused by one of several factors, but the most common faults that would account for them are either a bad ground or an overloaded wiring harness on the vehicle. Since you have tried your 2004 Ram Pickup with another trailer and have the same problem, I suggest you first focus on the vehicle for troubleshooting. The best tool for this is a circuit tester, such as # PTW2993.

First, you will want to test the Ram trailer connector for proper signals with the trailer disconnected. I have linked two articles on trailer wiring that show you which pins on your trailer connector should carry each particular light function as well as troubleshooting tips. There are diagrams for both 6-way and 7-pole blade connectors that show which light function should be carried on each pin. With a helper in the truck to activate the functions one by one, apply the grounded tester to each pin to see if the correct signal is present.

For example, if you have a 4-pole flat trailer connector (refer to the photo provided) you will ground the tester at the exposed ground pin and then test the pin for the green wire with the right turn engaged. Test the pin for the yellow wire with the left turn engaged. You should detect on-and-off blinking signals on these two pins. Next test the pin for the brown running light wire; here you should detect a steady signal when the Ram headlights are on. If you have a 6-way or 7-way on the truck you will do the same tests on the appropriate pins on those connectors. If you detect correct signals on the Ram trailer connector then the issue could be in your trailer connector or its wiring.

If you do not detect the correct signals then you will want to check your Ram wiring upstream of the trailer connector. If you are using a converter such as Curt # C55504, which plugs into your Ram taillight assemblies, you can test the wires going to the left (input) side of the converter to see if the vehicle is sending the correct signals to it. If not, check the connector contacts for signs of even slight greenish or whitish corrosion. Even slight discoloration can indicate corrosion that could interfere with proper operation. If the correct signals are going in to the converter but not coming out, then the unit may be damaged. You will also want to inspect any OEM connectors upstream of the trailer connector for signs of damage or corrosion on the contacts.

Pay particular attention to all ground connections on both the vehicle and trailer side. If the white ground wires are not firmly attached to a clean, rust- and paint-free surface there may be an inadequate ground that will not pass enough current for all light functions. Running lights draw more current than stop and turn lights; this is why sometimes the turn signals will work but the running lights will not.

If your trailer has a large number of running/marker lights, particularly the incandescent type that draw the most power, or if additional lighting was recently installed, then there may not be enough current capacity in the vehicle wiring or aftermarket harness.

I have also provided a link to our main page for wiring for your 2004 Ram. You can use the drop-down menu to select your vehicle style and see appropriate wiring products.