anyone have insight on how to disable the theft system once it has been enabled on a 98 mustang GT? I have reset the fuel pump in the trunk with no luck

 

i'm guessing you don't have a remote? i think...i might be wrong, but leave the door open....unhook the batt, rehook the batt, then i shouldn't go off because the door is already open, then hit the "valet" switch to supress til you get a remote

 

I'm going to assume it is the same anti-theft system that is in an 04 GT.

First off, you should have checked your manual, it explains it.

The theft system doesn't stay engaged. It reads a code in the key, if it matches what the car expects, everything is normal and the car will start. If it doesn't, the theft light will blink fast and when you try to start the car there will be no spark. Fuel delivery is fine, but with no spark, it won't start.

Either your key got messed up or the sensor got screwed up, either way it has to go to Ford because you can't modify that stuff yourself.

The key code is stored in the speeodmeter cluster, if you swapped that out, that is the reason it will not start, put the old one back in and you will be able to start it.