What do I need to do to my 2003 ford mustang to use the ecm from a 1995 mustang

You can’t, the 1995 is old school OBD1 and the 2003 is next generation OBD 2. Two totally different operating systems.

Answer not posting

I got some answers for yall 2 first off your wrong about that old system the94 and the 95 was eqipt with an obd2 port And Mr radiator cap guy...have you ever even worked on a car before they probably caught you putting your radiator cap on a empty milk jug full of something called your a total idiot..this is a serios question save your comments for that box at the front of the classroom for guys like you

The v6 which is what I got has obd 2 so can someone give some insight

The 03 is still a different OBD 2 operating system even if the 94 has OBD 2 it is not the same. A hot rod shop might be able to put you in touch with a programmer that can build you an ECM to do what you want but it won’t be cheap if you find one. The only other thing I can think of is if the blocks are the same you can swap 94 engine management hardware to the 03 engine making it compatible with the 94 ECM.

The problem with a 1995 model is it could be EITHER OBD I or OBD II. 1996 and newer is DEFINITELY OBD II and 1994 and older is DEFINITELY OBD I. The style of the connector that you're talking about makes no difference. That style has been used since the late 80s. My (OBD I) 1993 Caprice had one under the dash too. It was called the ALDL (Assembly Line Data Link) connector in those days . Hope that helps! Jim