Mustang battery retainer hold down plate.
In your Mustang the "battery hold down" is designed to do exactly what it's name implies, to hold down the battery. It does this by wedging itself against the base of the battery and the battery tray thus preventing the battery from moving around while you are driving. Don't drive your Mustang without a properly secured battery, not only is it much safer but it is required when you take your Mustang to the race track!
5.0 Resto - Dedicated To The Preservation Of The Fox Body Mustang
5.0 Resto® specializes in restoration and specialty parts for 1979-1993 Ford Mustangs. Using years of experience in the late model Mustang restoration and aftermarket industry, 5.0 Resto® is your source for anything Fox Mustang. While designing, and manufacturing several items such as 5-Lug Conversion Kits, weather stripping components and interior restoration items, 5.0 Resto® also uses many other name brand suppliers to provide problem solving products directly to the Fox Body Mustang community. As with any part branded as 5.0 Resto®, they stand behind all of these products to the fullest extent and have tested these products to ensure they live up to the quality and performance you have come to expect!