I recently installed a 7 way setup on my '02 Jeep Liberty, the memories of rust landing in my eyes are still fresh. Recommend safety glasses, corrugated nylon tube to protect your harness and circuit breakers vs. fuses for both the battery power at the 7 way and brake controller input. Look for circuit breakers with mounting tabs, makes things much easier.
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Rather than tapping directly off of the battery cable lug, locate the under hood fuse panel. There will be a heavy gauge wire direct from the battery that will terminate on a lug inside this panel. Use this lug to connect your leads. Follow the battery cable out of the panel so that the cover closes properly when you're finished.
Map your harness route wisely. Following the brake lines on any vehicle should be a safe bet as they are generally routed away from heat and vibration and have factory installed mounts to tie your harness to.
Keep your harness free of any joints; 1 continuous length of wire will flow current much more efficiently than a length with only 1 joint let alone multiple.
Apply dielectric grease at every point of connection to seal out moisture.