Trailer Running Lights Not Working Only When Starting Volvo XC90 Engine

Updated 09/16/2019 | Published 09/13/2019

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Question:

The running lights are not working as soon as I start my 2007 Volvo XC90. If I just turn on the ignition, everything works including running lights, brake lights, signal lights. As soon as vehicle is started, the brake lights and signal lights work but no running lights which can be disastrous at night. I have installed the harness just as the instructions indicate. I used the #118411 harness. The vehicle is equipped with daytime running lights feature and automatic turn on headlights at night. As mentioned, everything works are is should until the car is running. With just ignition on it running lights, signal lights as breake lights work - as soon as started the running lights do not work on trailer but brake and signal lights work. Loved the plug and play harness but have to figure out why no trailer running lights when engine started running lights on car work perfectly.

asked by: Leon S

Expert Reply:

I honestly haven't heard of this type of issue before. Just to be clear, when you just have the light on in your Volvo the trailer lights work perfectly but when you actually start the vehicle the running lights stop working?

If this is the case then the best thing I can recommend trying is testing the wires that are going to the black converter box on the Tekonsha T-One # 118411 with the vehicle running with a circuit tester like # PTW2992. Check to see if you are getting power on the running lights circuit with that function activated. If you are, then something may be going on with the converter box and it would need to replaced (it does come with a 1-year warranty).

If that checks out fine I recommend making sure the ground wire is securely attached to a clean bare metal surface. It's a long shot but it might be possible that the slight vibration from the engine running is knocking loose a weak ground connection.

Please let me know what you find and we can go from there.

expert reply by: Chris R