I have a 1989 F150 with dual gas tanks. And recently one of the fuel pumps went out, but I don't know if it was the high pressure or low pressure pump the went bad. How do I go about finding out which one it is or f it is both

 

It will not run at all if the high pressure pump is not working.
You can have someone turn on the key when you are under the truck and you should hear the selected in-tank low pressure boost pump and the high pressure pump run for one second each time the key is turned from off to on.
The high pressure pump is located on the frame.

Your fuel system:


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One more question, it seems like all three pumps have gone out at the same time. Is there a possible electrical problem with them or is it normal for that to happen? I have already checked the fuel pump relay and it works fine

 

Try resetting the Inertia Fuel shut off switch.

 

The answer is yes, you probably have an electrical problem. You have overlooked one important component in the circuit; the Inertia Switch. It is designed to remove power from the fuel system in the event of a hard impact. On your truck it should located near the driver side kick panel IIRC. The later model trucks 92+ it is located behind the passenger kick panel.

Keep in mind there will be no power to the pumps after the first 1-2 seconds when you turn the ignition key to the On position. Once you start to crank the PCM (engine computer) receives pulses from the stator (aka PIP) inside the distributor. This signal triggers the PCM to turn on the Fuel Pump Relay as well as starts the ignition process.

If you want to turn on Fuel Pump power 100% to diagnose your issue connect pins 2 & 6 on the Diagnostic Link connecter under the hood. Bil has some great info in this thread:

https://www.ford-trucks.com/forums/9...problem-2.html

 

The inertia switch is properly set, but the fuel pumps still arent working

 

If Inertia Fuel shut off switch is not tripped and the green bottom based relay is OK then check the wiring under the relay or if there is power on the yellow wire to the relay.