Troubleshooting T-One 4-Pole Wiring Harness 118425 in 2012 Jeep Grand Cherokee  

Question:

Expert Reply:

Thank you for your purchase of T-One 4-pole trailer wiring harness # 118425 which is a confirmed fit on your 2012 Jeep Grand Cherokee and installation of which is shown in the linked video on a 2013 model year GC.

Your issue of certain left-side vehicle lights now not working after you first connected your trailer suggests that your trailer either has a short-circuit somewhere in its wiring or that its total power demand from all of its lights is more than the harness can deliver. Either of these could cause a vehicle fuse to blow so first you will want to check the power distribution (fuse) box in the engine compartment (or elsewhere) for any fuse locations related to left side stop, turn or taillights. Your fix may be as simple as replacing a fuse with one of the same type and value.

If you have a circuit tester like # PTW2993 you can test the GC's trailer plug (without the trailer connected) to see if the lighting signals are making it all the way to the pins on the plug. You will need a helper in the car who can activate the light signals one at a time while you test the appropriate pins on the 4-pole plug. Please refer to the linked articles for the light functions that should be found on each pin and for troubleshooting help.

You can also test the disconnected trailer to see if its lights function properly independent of the wiring harness on the GC. You'll need a 12V power source like a spare car battery. You can connect the battery ground to the pin for the white wire and then one by one each of the other pins to the battery positive post. If the trailer lights behave normally when tested in this manner, then the issue is likely to be on the vehicle.

expert reply by: Adam R

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