Correct my previous post. It is Ford engineering part number C8ZB-14A301-A, bracket, as shown in the 1968 Mustang Electrical Assemble Manual (AM0023), used for mounting circuit breakers used for fog lamps (pg53), safety convenience group (pg56) and air conditioning (pg83). Strangely, the 1968 bracket does not appear in the 1975 Ford Car Parts (aka MPC), but is in the 1960-68 edition (C8ZZ-14A301-A, as do two variations used in 1967).
Jim