Acc-Batt fuse on 94 Blazer

[usar17]

I got the woring harness installed in my truck from a 1500 blazer. I just noticed the 30amp....breaker (?) was hot in the fuse panel. I pulled it and the truck still started. Radio worked. What all runs thru that and could cause this? Truck was sitting for 2 days and was still not running when i noticed it. Checked for a parasitic drain and didnt see any amp draw.

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208