Why Does Trailer Wiring Harness Need to be Connected to Battery on a 2010 Mazda CX-9

Question:

What’s the need to run to the battery directly? Wouldn’t it work just fine from connecting the T connector from the OEM lights on the vehicle? Is the battery connection for trailer brakes?

asked by: Steve

Expert Reply:

Trailer wiring harness # 118520 for the 2010 Mazda CX-9 is a powered converter. This means it requires a direct connection to the vehicle battery to power the trailer lights. The T-connectors provide the proper signals to the converter and trailer lights. The powered converter is required in order to protect the sensitive wiring on the vehicle. If there were a short it would blow the fuse or converter and not damage the vehicle electronics. The harness will not work unless it is connected to the battery.

I have linked a video showing a typical installation for you. I have also included a link to an FAQ article I wrote with tips on connecting to the battery.

expert reply by: Michael H