Troubleshooting Installation of Tow Ready Wiring Harness on 2016 Toyota Highlander

Updated 05/13/2020 | Published 05/16/2016

Products Featured in This Question

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(1124)

$45.90

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(942)

$46.68

Adapter 4-Pole to 7-Pole and 4-Pole

(659)

$61.64

Hook Probe Circuit Tester

(60)

$12.41

Question:

I purchased a C56217 for my 2016 Toyota Hylander and installed it no problem. I connected the 4 point harness to a 7point. It appears that the running lights do not come on, when I turn the switch to lights on. The turn lights, flashers, and brake lights come on although the brake lights seem dim daylight hours. The video shows a separate ground wire, which it appears to be obsolete. Also, my fuse box says tow 30amp and the kit came with a 10amp. Any suggestions?

asked by: Barry

Expert Reply:

The Curt Wiring Harness # C56217 does have an external ground for the converter box harness that would need to be grounded to the vehicle's sheet metal. However, when I checked your order, you ordered the Tow Ready Wiring Harness # 118449 and this wiring harness does not have a ground wire that needs to be grounded separately.

To begin troubleshooting, I recommend using a circuit tester, # PTW2993, to test the 4-Way connector of the # 118449 harness. I've attached a video showing how this is done. It is easiest to have a buddy inside the vehicle to activate the functions of the harness while you test the connector. The pin connected to the brown wire is the one that carries the taillight function. This pin should show a constant signal when the vehicle's running lights are on.

It sound like you are using a 4-Way to 7-Way adapter, like # 37185. If this is the case, I recommend first testing the original 4-Way connector and then plugging in the adapter to test the running light pin on the 7-Way. When holding the 7-Way socket's lid open, the running light pin is located in the 11 o'clock position. If the running lights work on the 4-Way connector but not on the 7-Way adapter, there is something wrong with the adapter.

If the running light circuit tests correctly on both of these connectors, the issue is on the trailer. You will want to check for damage or a cut wire on the trailer's running light circuit that would cause the lights to not work. Corrosion or a tear in the wire touching bare metal can cause issues for trailer lights. Checking inside a 7-Way connector for corrosion is also a good idea. You will want to check and make sure the lights are properly grounded to a clean, bare metal spot on the trailer.

If the 4-Way connector of the # 118449 harness does not test for power on the running light circuit, there are a couple of other places we will want to check the circuit. You will want to test the wires for the running lights on each side of the vehicle wiring harness's black converter box. The brown wire on each side of the converter box should show signal with the circuit tester when the vehicle's running lights are on. If the wire going into the box shows power, but the wire coming out of the box doesn't show power, then the converter box is not working properly.

Since you said the other light functions are working, this indicates both 10 amp fuses are working properly. It will not cause any issues to have a 10 amp fuse in a 30 amp fuse spot for this wiring harness. This means the slot can accommodate a 30 amp fuse, but for this harness only a 10 amp is required because the harness is designed to only draw a maximum of 7.7 amps. Using a smaller amperage fuse means the fuse will be blown by an amperage over 10 rather than an amperage over 30.

If none of these troubleshooting steps provide a solution for you, please feel free to let me know and we can take further troubleshooting steps.

expert reply by: Victoria B

Robert D.

5/7/2020

I install a curt 56217 wire harness I have no tail lights

Chris R.

5/8/2020

Have you tested the 4-Way itself for power on the tow vehicle? It could be an issue on the trailer side. On the vehicle end just be sure the connections are securely plugged in and that the ground wire is attached to a clean, bare metal surface without any corrosion or debris preventing a good attachment. On the trailer side make sure the lights themselves are still securely grounded as well. Let me know what you find and we can go from there if the issue persists.

Robert

5/8/2020

@ChrisR Yeah I checked all the wiring nothing everything seems right I hooked up the trailer to my buddies truck everything works normal on the trailer

Chris R.

5/11/2020

@RobertD Thanks for the info - we at least know the issue is on your Highlander. There might be a blown or missing fuse under the hood (check your owner's manual for the location). If that checks out okay I would try testing the converter - test the wiring going to it to see if you get power on the running lights circuit, and then power on the wiring after the converter. If you lose power in between the converter is bad and would need to be replaced (under warranty).