Ford computer runs the fuel pump.
Fuel pump should only get 12volts for 2 seconds when key is first turned on, it's a safety feature.
Fuel pump won't get power again until engine RPMs are above 400, OR unless you turn the key OFF and then ON again, then it will come on for another 2 seconds.
Fuel pump relay
yes in its plug in there should be 1 slot with 12volts all the time, key on or off, that from the fuel pump fuse.
Then there will be another slot with 12volts but ONLY when key is on.
The computer controls the Ground for this relay, so even though it gets 12volts when key is on it can't "activate" until it is Grounded, computer does that, for 2 seconds.
To test if relay is working you will need to find the OBD1 connector, usually near firewall drivers side, by power brake booster.
It just hangs loose in main wiring harness.
Drawing of it here: Ford Ranger - Testing EEC-IV Equipped Engines
In the drawing you will see a slot in that connector labelled Fuel Pump.
That is the Ground for the fuel pump relay, it is spliced to the computers wire used to ground the relay.
So find it
Turn on the key
Put a jumper wire in that slot and ground the other end
Relay should "click" closed.
You can leave jumper connected, doesn't hurt anything, same as if engine was running.
That should give you full 12volts at inertia switch for testing and at the connection by the gas tank.
When you are testing voltages you have to keep in mind what is connected to the wire(s).
If powered you will see 12volts going into and coming out of a motor, like a fuel pump, that's because a motor is just a long wire, voltage in voltage out, what a motor or light bulb for that matter, needs is 12v AND a ground, then it will run.
For example if you where to test for voltage on that fuel pump slot in the OBD1 connector when key was on it would show 12volts, thats the power passing through the relays coil of wire, but relay doesn't close until it is Grounded.
Sender in gas tank runs on 5 volts, it comes from the dashboards pulsed 5v power supply
Here is a 2.3l wiring diagram for engine wiring: http://www.therangerstation.com/tech...ls2_3_1of3.JPG
Upper middle is fuel pump relay
VIP test connector is the OBD1 connector
yellow wire is from the Fuel gauge to the sender
Orange wire is the Ground for the sender
Pink wire is fuel pump power
Black wire is fuel pump ground
Also because Computer monitors if Fuel pump is getting power you will always read some voltage at inertia switch when key is on, that is from the "monitor" circuit, not the Fuel pump Relay, you will read full battery voltage when relay is close.