Troubleshooting Trailer Wiring Malfunction in 2000 Lincoln LS

Question:

Had a trailer hitch installed including the wiring harnes. My new trailer driver side brake light will illuminate after half hour after being shut down ? I would open the car door and trailer light would go out...then back on in about half hour after closing the door. wtf

asked by: Darrell L

Expert Reply:

The wiring harness we offer for your 2000 Lincoln LS is part # C55373 from Curt, it has a 12V power wire that needs to be run up to the car's battery to deliver the actual power for the trailer lights. The Curt harness you referenced, part # C56160, works the same way, although it is NOT a confirmed fit for your 2000 Lincoln LS (it fits the MKX only). Hopefully this is not the harness that was installed.

Based on the (very) odd behavior of your trailer's driver-side brake light, it sounds like either there was a wiring error during installation or the harness converter box has shorted out. Shorts usually arise on the trailer side and it is entirely possible that a problem on the trailer took out the harness.

I suggest you disconnect the trailer from the LS and test each separately. This is easy to do. First test the trailer by connecting its lighting circuits, one at a time, to a 12V battery (you can use the one in the LS or a spare if you have one). If the lights on the trailer behave normally when powered in this manner then this suggests the problem is in the harness.

On the vehicle side you can test the harness using a circuit tester like # PTW2993. Disconnect the trailer and have a helper activate a lighting function, say the brake pedal, while you test the green and yellow wires. These wires carry both brake light signals and turn lamp signals. When the brakes are engaged the green and yellow wires should carry a steady signal as long as the pedal is pressed. When the right turn signal is on the green wire only should carry an on-and-off blinking signal; same for the left turn and yellow wire.

If the harness behaves normally when you test it (with no trailer) then I suggest you check the harness white ground wire. The ring terminal for that harness must be tightly affixed to a clean bare metal spot on the car. Weak grounds can cause all sorts of weird behavior from trailer wiring. It is very easy and costs nothing to confirm the ground is good; odds are also good that this will fix your issue. If not, then please let me know the results of your testing.

expert reply by: Adam R