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Turn Signals on Trailer Do Not Work When Towed By a 2006 Toyota Tacoma

Question:

I installed a T- connector harness in my Tacoma to run the lites on my traialer. It worked for 2 or 3 years then one side stoped blinking. I purchased a new harness and it does the same thnig. The lites and blinkers on my truck both work.

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Expert Reply:

The first step that I would take to troubleshoot this issue is to test the 4-way connector on your 2006 Tacoma for proper function. This will tell us if the issue is on your Tacoma or on the trailer. First, make sure the new wiring harness is properly grounded. It should be connected to a clean, bare metal surface on the vehicle frame or to the negative terminal of the battery.

If the ground connection looks fine, you will want to use a circuit tester like part # 40376 to test each pin on the 4-way connector for proper function. I attached a video of my co-worker using this circuit tester to test a 4-way connector for you to check out.

If the 4-way connector on your Tacoma is functioning appropriately, then we know the issue is on the trailer. Again, first check for proper ground connections for the trailer side 4-way connector and the trailer lights. Poor ground connections can cause a number of issues. Make sure there is no corrosion on the ground connections and that they are connection to clean, bare metal sections of the trailer frame.

If the ground connections look okay, hook your trailer to your tow vehicle. Have someone activate the tail light functions and test each wire at the 4-way connector and locate the wire for the side that is not working properly. Using the circuit tester, probe that wire just past the trailer connector to see if power passes through the connection between the trailer and tow vehicle.

If you have no power on that wire, the issue may be in the 4-way connector itself. If you do have power past the connection, work your way toward the tail lights probing the wire. Also look for sections that may be pinched, frayed or damaged that could cause a short. This will tell you where the power terminates.

I have attached a trailer wiring diagram for you to use when troubleshooting your trailer wiring. I have also attached an FAQ article on trailer wiring for you to look over. If you are unable to find the issue or a solution after following these steps, let me know what you come up with and we can take further troubleshooting steps.

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John H

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