NHTSA Complaint #11561232 — 2023 MAZDA CX-50

After installing Mazda Genuine Accessory 4-pin trailer wiring harness (P/N VA40-V7-780A), and Mazda’s trailer hitch as well, found that the wiring does not operate correctly. When the turn signal or hazard lamps are activated while the brake is applied, the trailer lamps will operate erratically, flashing faster for a few cycles, then return to a normal flash rate before the erratic behavior repeats. The Mazda’s lamps operate normally. This has occurred with two different trailers, one with incandescent and one with LED lamps. To verify that the concern wasn’t with the trailers, a small trailer-side harness was made that used a floating ground, and with either incandescent or LED stop/tail/turn lamps plugged into it the concern was the same. Dealership verified the concern and verified correct installation of the vehicle harness. They were able to replicate the concern on another CX-50 as well. They reached out to Mazda’s technical assistance, but have not been advised of a repair. This was several months ago. Mazda’s customer service was of no help. May not be compliant with FMVSS No. 108, S14.9.3.5.3, S14.9.3.9.3, and Figure 2. Concerned that this may increase the risk of another vehicle striking a trailer attached to the Mazda. The vehicle is available for inspection upon request.