On a '81, the idle control unit is directly behind the glovebox, and the overload relay is in the passenger kickpanel.

There isn't a replaceable fuse on the '81 overload relay, only a fixed one. Mine was blown which causes high idle speed. You can solder a standard 10 amp fuse across the open fixed fuse if yours is blown, or solder a fuse socket in so you can change out fuses in the future.