No Running Lights on Trailer When Using Tow Ready T-One Harness 118384 on 2004 Chevy Silverado

Question

Question:

I recently bought a 2004 Chevy Silverado. I went to plug my work trailer in and only my right blinker and brake light would work. I noticed the factory installed 7 prong trailer attachment on the truck was a bit corroded, so I bought a new one. Now all the lights work except my running lights on the trailer. I did check the fuses under the hood and they all seemed okay. I am stumped..could it possibly be a bad ground? I have a voltmeter, is there a way to test to see the issue?

asked by: Shawn W

0

Expert Reply:

Since you have replaced the factory 7-way connector on your 2004 Silverado due to corrosion you may also want to check the condition of the pins on the round vehicle connector under the rear bumper. This is the connector that mated to the original factory 7-way socket and that may now mate to the T-One Harness # 118384 if you are using this part. Since the outside contacts on the 7-way were corroded it is also possible that the other upstream connections may need cleaning as well.

Even a very slight greenish or whitish discoloration on the contact surfaces could inhibit signal transfer. You can use a spray-on contact cleaner as needed. Check also that the contacts themselves are not bent and that the wires leading to them are not loose. Once your connections are confirmed as clean and solid a protective coating of a dielectric grease such as # 11755 will help to keep them that way by discouraging the entry of water and dirt.

You can also use your voltmeter or a circuit tester such as # PTW2993 to test the running light function at the vehicle connector (without the trailer connected). Running light signals are usually carried by a brown wire. Use your voltmeter or circuit tester to confirm that there is a signal on the pin corresponding to the brown wire when the Silverado headlights are on. On a 4-pole connector the running light pin is next to the ground; on a 7-way it is the pin located at the 11-o-clock position as viewed from the rear of the vehicle. Please refer to the two photos provided for illustration. If you confirm a steady voltage on the appropriate pin when the vehicle lights are on then the issue may be in your trailer wiring.

Start by inspecting the trailer side connector for the same signs of corrosion and/or damaged or loose contacts. Verify that the white ground wire from the trailer connector is firmly affixed to a clean rust- and paint-free metal surface on the trailer frame. (You can use fine sandpaper to help clean the area for the ground connection.) Sometimes a weak ground will pass just enough current to allow turn signals to operate but not enough for running lights which draw more power. Last you can check the wiring at the tail light assemblies for clean solid connections.

If you have an opportunity to try your truck with another trailer (and/or try your trailer with another truck) you will be able to first isolate the issue to the tow vehicle or trailer. You may also want to refer to the linked article which includes additional hints on troubleshooting trailer wiring.