Falcon 170

I can't remember how I got the pic to post ,the thing I am trying to figure out is a electic box that has fins and 3 -10 ga. wires. The van would not charge and after checking pos.post on alt. it had the factory wire and a 14ga.wire that looks like someone added later the 14ga.wire was beside the battery not hooked up factory pos.wire on alt. is not hot so I checked fuseable link on the wire that go's from starter to alt.it is good come to find that wire that normally go's to alt. go's to this box and 1 wire from box go's to alt. the other wire go's to battery in rear I thank this box is to charge the rear battery