Troubleshooting Trailer Running Lights Operating at 5 volts With Curt 4-Way On a 2019 Mazda CX-5

Updated 12/07/2022 | Published 12/06/2022

Products Featured in This Question

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(138)

$69.57

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(201)

$75.53

Digital Multimeter with 42" Long Test Leads - XL LCD Display

(5)

$40.47

Question:

This worked fine with our trailer for 2 days, but then the running lights/tail lights stopped working. When I turn on the headlights, the running lights blink very briefly and then go out. When using a plug in tester, it shows that the TM output is working, but weirdly shows that it is getting power whether the car is running or not, and whether the headlights are on or not. This is unexpected. Using a multimeter on the correct pin, it appears to show an output of 4v when the car isn’t running, and 5v when the car is running. I’m thinking it should be 0 when the car isn’t running, 0 when the car is running but the headlights are off, and then 12v when the headlights turn on? I called Curt, and frankly they were defensive and not very helpful, mostly blaming the trailer.

asked by: Josh L

Expert Reply:

You are correct that there should not be any power to the running lights/tail lights when your headlights and running lights are off on your 2019 Mazda CX-5. It sounds like you have a short in the wiring. You can use your Multimeter # PT29ZR to test the power going into and out of the Curt T-Connector # C56377. This is the most likely culprit as the only power inputs on the trailer for a 4-way are the running lights, brake lights and turn signals.

If Curt is unhelpful for resolving your issues and you are out of the factory warranty I recommend switching to the Tekonsha T-One # 118746. In my experience the Tekonsha converter module is more durable and develop less issues over time.

expert reply by: Bud M