Troubleshooting a 7-Way Trailer Connector on a Toyota Sienna  

Question:

Expert Reply:

The first step I would take is to inspect the vehicle side and trailer side connectors for corrosion and clean or repair as needed. I would also recommend checking the ground wire for the trailer connector. Make sure the ground is not loose, rusted or corroded. We have found that corrosion and ground problems are the culprit almost 90 percent of the time.

If corrosion or a poor ground do not seem to be the problem, then we will want to inspect the wiring harness. The Toyota Sienna never came with a factory tow package that I am aware of, so I would bet that the problem is with the tail light wiring harness. Since the Sienna has a separate tail light wiring system, meaning the brake light signal is separate from the turn signal, your Sienna would have required a trailer wiring harness with a converter. These converter boxes will short out if the trailer wiring harness shorts out or if it detects a short on the trailer.

To see if the converter box is the issue, you will want to gain access to the converter box. On the Sienna, the converter box is typically stored behind the one of the interior trim panels in the rear cargo area. It could be on the drivers side or passenger side depending on the model year of the Sienna.

Once you locate the converter box, you will notice that there are 5 wires on one side and only 4 wires on the other. The side with 5 wires is the input side from the taillights. Using a circuit tester, like part # PTW2993, probe the wires going into the converter box while a helper activates each of the taillight signals. The brown wire is for the running lights, green wire for right turn signal, yellow wire for left turn signal, red wire for brake lights and the white wire is ground. On the output side, brown is for running lights, green is for right turn/brake light, yellow is for left turn/brake light and white is ground.

If you have power going into the converter box, but not coming out, then the converter box has probably shorted out and will need to be replaced. If your Sienna is a 2011 or newer, there is a power wire that runs from the converter box to the vehicle battery. At the battery there should be either a red or yellow fuse holder with a 10 amp fuse inside. If the fuse is bad, you may just need to replace the fuse.

If you can tell me the year of your Sienna, I may be able to give you better instruction on how to access the converter box.

expert reply by: John H

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Terry

6/19/2014

It is a 2008 Sienna. Can up update the page with anything more particular to a 2008? Thanks, I think you are on the right track but I am not sure how to get to that convertor box. It is definitely in the vehicle because when I used a circuit light tester on the 7-pin plug, there was nothing coming out of any of them with the lights and flashers on.

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John H.

6/19/2014

Thank you for responding. On the 2008 Toyota Sienna, the converter box should be on the passenger side of the vehicle behind a small access panel. Check out the installation video we made on a 2008 Sienna. It shows where the converter box is located and how to access all of the trailer wiring inside the vehicle. The 2008 Sienna did not require a powered converter, so I think the problem may be the converter box. Once you find the box, test the wires as described above. Since you have a 7-pin plug, the wires from this harness were likely routed to the outside of the vehicle. I recommend checking the connection point between the 4 wires coming from the converter box and the 7-pin trailer connector also.

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