No Trailer Lights Using TowReady T-One Vehicle Wiring Harness for 2008 Volkswagen Jetta  

Question:

Expert Reply:

There are several potential causes for the problem you are having with the trailer lights not operating. The best method to troubleshoot is to first determine if the problem is on the vehicle side or the trailer side.

You can start by disconnecting the Jetta from the trailer. Apply a circuit tester such as # PTW2993 to the pins on the vehicle 4-pole connector while a helper activates the various lighting functions one by one. Please refer to the linked photo that shows the functions carried on each pin of the 4-pole. With the tester grounded apply the probe to the pin for the brown wire; this should carry a steady signal only when the Jetta headlights are on. Next apply the tester to the pin for the yellow wire; this should carry a steady signal when the brake pedal is pressed and a blinking on-and-off signal when the left turn signal is activated.

The pin for the green wire should carry a steady signal when the brake pedal is pressed and a blinking on-and-off signal when the right turn signal is activated.

If you detect these signals then the harness is working and the issue is in the trailer-side connector or wiring. If these signals are not present on the 4-pole then you can troubleshoot the harness installation by checking that all the electrical contacts within the connectors are clean and free of any discoloration. (Corrosion can appear as thin greenish or whitish film; contacts do not have to look rusty to have a corrosion issue.) Check for bent or damaged contacts. Make sure all connectors are fully seated and that the locking tabs are engaged.

Next re-check the white ground wire (with the ring terminal attached) to ensure it is tightly affixed to a clean bare metal surface behind the tail light assembly or to an existing grounding point. This ground wire must make very solid metal-to-metal contact with the vehicle.

You can next check the +12V power feed to the harness. Confirm the butt connectors at both the wiring harness and fuse holder ends are solidly attached to the supplied 12-gauge power wire. Verify that the fuse is not blown and is in place in the supplied holder. Confirm the other lead of the fuse holder is firmly connected to the battery positive terminal.

If these steps correct the problem I suggest an application of dielectric grease on all connections to ensure they remain corrosion-free for as long as possible. For reference I have linked an article and video concerning 4-pole troubleshooting that may also be helpful to you.

expert reply by: Adam R

0

click to enlarge