Exhaust 1995 ford mustang gt 5.0 header question

The other way to trick the EGR is to stick the plunger down half way permanently. Will usually let the CEL turn off the majority of the time, ran my car like this for long time.

@Labora is correct, though you'll have a different EGR code if you do that, but at least it doesn't light up the dash. Best way is to keep the system intact as it actually does significantly lower your NOx emissions and also allows you to run more advanced timing without pre-ignition than without it. It, along with the catalytic converters, are two emissions components that are actually pretty effective. It is very possible to get great results while still being environmentally conscientious (high flow cats are inexpensive and hinder flow very little). My turbo 95 passes its tailpipe test every other year with flying colors. I understand not everyone cares though or has emissions testing, but you probably devalue your car by stripping those bits off as no one in another state or county that has emissions testing will want to touch it. Probably not a big deal with KBB on our cars <$3k.

Barring that, there is a flag that can be set in a tune which just shuts the whole thing off. A 'tune' on an SN95 Mustang requires a piggy-back chip to be added to the ECU which contains a modified set of runtime parameters for the stock computer to use. It requires someone to write that tune to the chip before you install it. Common solutions are SCT chips (often with Bama tunes) - check American Muscle for details, and Moates Quarterhorse with your own tunes written by Binary Editor. Other free software and lower cost chip options exist.

In your case though, if entirely stock, a tune and chip will cost a few hundred bucks. I'd repair the EGR system instead and look for headers that support it, or perhaps have them modified to support it. But if you really don't care, the half-pushed-in plunger attached to the harness will work fine.