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1989 Ford Mustang:
Fuel Pump Not Shutting Off - Bad Relay

Alex Steele
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I have a 1989 Ford Mustang LX and I have a problem with the fuel pump not shutting off. It continues to run until the battery goes dead. I pulled all the fuses in the fuse panel under the dash on the left side, but the fuel pump didn't stop.


I can hear a hissing noise in the engine compartment as if the pressure were relieving. Any temporary suggestions? Maybe installing a toggle switch or pulling a fuse somewhere while the car isn't running would help.




Why don't we go right to the source of the problem and disconnect the system there? Look underneath the driver's seat for a relay with a tan & light green, an orange & light brown, a red & black, and two pink and black wires coming out of it. This is the "Fuel Pump Relay" which is a good chance of being the cause of your problem.


Disconnect it and you'll no longer hear the fuel pump running with the ignition off or the "relieving" noise you've described coming from the "fuel pressure regulator" under the hood. Then go straight to the parts store and purchase a replacement relay which will eliminate your need for jumper cables every morning.


The sticky relay has been a common problem on several Ford vehicles. So, I pulled up the applicable Ford Technical Service Bulletin #90-18-3 with the aid of the ALLDATA information system. The part number for a genuine Ford Fuel Pump Relay is F19Z-9345-A.

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