Troubleshooting No Running Lights with Trailer Wiring Harness Installation on 2013 Toyota Sienna

Updated 06/16/2015 | Published 06/13/2015

Question:

I have installed the wiring harness from you guys for my 2013 Toyota Sienna and the tail lights on the trailer will not work. Everything else works fine. When I put a volt meter on the tail light port on the 4 prong it only reads 4 volts. Ive got a GMC Canyon that I also can hook up the trailer to and the trailer lights work fine. So with my van only reading 4 volts, Im guessing thats the issue? Can you please help me with this issue? Thanks

asked by: Mike

Expert Reply:

I could not find purchase history for you to confirm which wiring harness you have but the linked page will show you those we offer from Curt and Tow Ready, parts # C56106 and # 118498.

The most common cause for some lights (in your case stop and turn) to work but not running lights is a bad ground connection either on the vehicle or on the trailer. Since running lights stay on they will draw more current than blinking turn signals or brake lights that are often on for short times. A weak ground will let some functions work normally while others do not.

Check the wiring harness white ground wire were it attaches to the vehicle to ensure that it is solidly attached to a clean bare metal surface. Clean that spot or sand off the paint if needed to enable a good connection. Also check for any dirt or slight greenish or whitish discoloration on the contact surfaces and clean as needed.

If the ground is good and the vehicle's own tail lights work properly on their own then the harness may be damaged.

expert reply by: Adam R