The 12v positive wire from the reducer would be the wire you use to feed 12v power to the fuse block. Get a fuse block that uses one stud for the fuse block feed.
Something like this.....
OLS 6-Way Blade Fuse Box [LED Indicator for Blown Fuse] [Protection Cover] [100 Amp] - Fuse Block for Automotive
https://www.amazon.com/dp/B00QMTAZ1W..._eczFAbHCQK59A