The 86 will be the grounded side of the relay coil. 85 will switch the relay on and off (switched power). The 8 gauge wire seems extremely large for supplying power to your accessories since it is rated at 40 amps. I recommend adding the total current draw for all components then verify that the relay you plan on using can handle the load. Also there will be an instantaneous current rush at power up so the circuit should be rated at 125% of the total calculated load. Good luck