I'm guessing it's a disconnect switch, but it's hard to tell. Not sure why there would be 4 nuts on it. At first I thought it went from one battery post to the other, but then I realized the red wire at the top just passes under the black wire.
It could also be part of a current sensing circuit. The extra two connections would go to an ampere meter of some sort.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10