How to MOSFET to drive 12v relay from microcontroller (logic high is 3.3V) using ZXMS6004FF
Your MOSFET is connected upside down.
The Source pin shound be connected to "ground"/0V and the Drain pin should be connected to your relay/"BRAKE_LSD_3".  

Remember that most MOSFETs have a "body diode" in parallel with the Drain and Source.
If you look at the symbol of your MOSFET you'll see a little arrow in the middle - that gives you a hint as to which way the diode will allow current to flow through the MOSFET no matter whether its turned on or off.