Nothing like you describe in the accessory manual so guessing it is something a PO has added for some reason. Maybe some pics of it will generate ideas as to what it is and may have been used for.
Bruce


Bruce
Old Toy: Ol' Betsy stock 59 Apache SB Stepside (Gone but not Forgotten)
New Toy: 1962 Impala SS Coupe
The Driver: 1990 Toyota truck