Troubleshooting Left Stop/Turn Lights that Failed at Same Time  

Question:

Expert Reply:

In trailer wiring, including a 4-pole harness such as the Curt kit # C59236, the stop and turn signals for each side of the trailer are combined together into a single circuit. Both of the functions on your trailer failing at the same time is a result of them being carried on the same wire. In 4-pole wiring the YELLOW wire carries the left stop/turn signals.

First you can check your fuse/power distribution box for a blown fuse or relay that is assigned to the left stop/turn light circuit. If the car's own left stop/turn light still works then you can skip this and just apply a circuit tester like # PTW2992 to the wire that is connected to the left tail light assembly. This will tell you whether or not the car's own left stop/turn signals are entering the harness module. If these signals are going in to the module but there is no signal coming out on the pin for the yellow wire then the harness may be damaged from a short-circuit on the trailer and it should be replaced.

But if the car's left stop/turn signals are NOT going into the harness on its yellow wire then you will want to check the quick-splice connector to make sure that connection has not failed.

You can also check the condition of both the vehicle and trailer plugs looking for signs of corrosion or other damage. Even slight corrosion on the contact pins can degrade the connection enough to block the signals. There are spray-on contact cleaners like Caig De-Oxit but you can also try a solvent like isopropyl alcohol and some fine sandpaper to remove any grease or corrosion from that pin.

You can also test the trailer directly by disconnecting it from the vehicle's wiring and applying 12V power from the car's battery directly to the trailer plug's pins. The photo included for you shows where to apply the ground and hot connections from the test battery.

expert reply by: Adam R

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