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Troubleshooting the Brake Light Not Working on a Trailer Hooked up to a 2016 Toyota Land Cruiser


I have hooked the trailer to a Mercedes Benz GL450 2015 and all the trailer lights (Brake, Tail, Signals) functions work properly. The car is equipped with from the dealer with the 7way connector near the hitch. I used this car to diagnose if the issue was is the trailer, but apparently the trailer wiring is fine. This is not the vehicle I want to use to tow my boat. I want to use Toyota Land Cruiser 2016 to tow the boat. I have located the wires for the lights on the back of the car (Brake, Tail, Signals) and fished the wires next to the hitch to connect it to a 7-way connector. The wires locations that I tried to use: - Left signal wire from the left signal light - Right signal wire from the right signal light - Brake wire from the right brake light - Tail light wire from the right tail light I connected the four wires from to the 7-way connector for each one as mentioned in the 7way connector description manual. All the lights worked except for the brake. The brake is not linked in anyway to the left and right signal wires in the trailer. It is only connected to the blue wire that is coming from the brake system in the trailer. The ground wire for the 7way connector in the car is attached to the car body. The only issue that I have is I want to connect the brake light to the right and left signal in the trailer to make it work. Please correct me if I am wrong because this is what I understood from what I read on the internet. I don't know if and adapter or a converter will help resolve the issue.


Expert Reply:

The problem that you are facing is that your trailer is running the right turn/stop on one wire, and the left turn/stop on a separate wire; otherwise known as a 2-wire system. Your 2016 Toyota Land Cruiser has a 3-wire system where the left turn, right turn, and stop wiring is run on separate wires.

What you will need to do is use the Tekonsha Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness # 119190. This wiring harness will combine your stop signal with your turn signals on your Land Cruiser wiring harness to give you the left turn/stop, and right turn/stop 2-wire system that your trailer uses. You will need to run some wiring # 118151 up to your battery so that the ModuLite has power.

I don't know what kind of 7-Way wiring harness that you already have, so I will give you some options. If you have a 7-Way that requires you to hardwire the appropriate wiring in, like part # HM48470, then you will need to connect the right turn/stop on the 3 o'clock pin, the ground to the 7 o'clock pin, the left turn/stop to the 9 o'clock pin, and the tail/running lights to the 11 o'clock pin. All of the pin positions are as if you were looking at the wiring harness from the front.

If you would like to use a brake controller, like the Prodigy P3 # 90195, for electric brakes or for an electric-over-hydraulic brake setup on your trailer, then I recommend using the # ETBC7 Wiring Kit. This will give you all of the wiring that you need so that you can get power to all of the lights on your trailer, and send the signal from the brake controller.

I have attached a helpful article about wiring for a 7-Way that you can reference.

expert reply by:
Jon G

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