Nitrous_bob, that isn't a relay, it's exactly what you said, an interia cutoff switch. If you get in a major accident, it cuts the fuel pump so fuel doesn't end up spraying everywhere causing more of a problem. How long does the pump run for after you take the key out? I could only imagine that if it stays on for good, you will end up with a dead battery in a hurry.

I don't know where the relay is, just clearing up some of the misconceptions.

 

You are exactly right - my daughter also has a 1989 Ford Mustang Convertable. We searched it high and low for the fuel pump relay. The fuel pump continued to run after the car was shut off, running the battery down to nil. The relay was located under the driver's seat, mounted to a metal bracket, just like you stated. The relay needed is E3EB 9345 B2A, which is the same as the relays required for the convertable top.

Hope this saves some other poor soul from a day of fruitless seeking, Chilton's manual was no help with this.

 

I just had a problem with my 89 convert. The fuel pump did not engage so I went to the inerita switch, reset it and began the long look for the relay. I didnt find it and the the car started. But I planned to look for the relay this weekend until I stumbled on this excellent forum. Thanks for the help also. I hope that the relay is bad and not the fuel pump or the interia switch.