R Dow

I just recently bought the truck. It has the auxiliary battery, there is a large red cable that feeds to the relay and then over to the passenger side battery, but the smaller red wire with green tracer is connected at the battery via a 30 amp fuse. Where can I find one of these in the aftermarket? Sort of looks like a 30 amp midi fuse. Not sure what it feeds, if I had to guess I'd say it feeds power to trailer aux/charging. I had a snow plow installed today and the installer told me that fuse is burned. Thanks