Replaced the fuel pump and there was only 7 volts getting to the pump so i traced the wires back and went to the inertia switch. There was 7 volts there so i ran a new power wire for the pump from the inertia switch to under the relay. It started and ran but then died but still the lights and radio died. What could be wrong?
1998 Ford Ranger 3.0 4x4

 

Welcome to the forum

With key on engine off, fuel pump voltage will show 5-8 volts all the time, it has no AMPs just volts, its from the computer's monitor circuit, so ignore this as "fuel pump voltage"

When you first turn the key on you should see 12volts(Battery Voltage) for 2 seconds, that happens each time key is turned from off to on, i.e. each time computer reboots
This is done to "prime" the fuel system, but only for 2 seconds, its a safety thing

Fuel pump won't get full time 12volts until engine RPMs are above 400, engine started
The safety thing is that in an accident if a fuel line breaks the engine would stall and fuel pump would STOP pumping fuel that may feed a fire

You can cycle the key on and off as much as needed to see if pump is working, you can HEAR it in the gas tank, it is not quiet

Power path for that 12volts
Battery--------------fuse--------Fuel Pump relay-------------------------inertia switch--------------------------------fuel pump-----------ground

Fuse #9 in 1998 Ranger engine fuse box

 

I could not hear the fuel pump turn on at all. Ill check the fuse again too

 

If you didn't buy a Motorcraft(Ford) fuel pump, then chances are the new pump was bad out of the box, not uncommon, have to go thru a few usually, to get a good working one

You can hook up a test light or volt meter in the cab to the inertia switch to see if you have the 12volts for those 2 seconds with key on, if so Pump is bad, if not then fuse or relay is bad

 

I ran a new power wire from the relay to the inertia switch and it worked. The the fuel pump fuse blew when driving so i replaced the fuse and the today the fuel pump fuse blew when i was driving again. What is wrong now do you think>

 

Did you disconnect/cut the old wire from both the FP Relay and the inertia switch?
If it wasn't working then it may be partially shorted so if still connected at either end it could cause fuse to blow

If a fuse doesn't blow instantly then you don't have a direct short to ground, it can be a corroded connection that heats up when used and eventually causes AMP draw, with Fuel Pump running, to cause fuse to blow

Could even be the fuel pump itself

Should be a 20amp fuse for a fuel pump, they can pull 11amps on start up and then pull a steady 7amps when running

 

i Cut both ends of the old wire and ran a new one. It doesnt blow right away it takes an hour or less then in blows.

 

I would test fuel pump OHMs

There should be a Pink wire on the inertia switch, that wire runs to the fuel pump connector on the top of the gas tank
Set ohm meter to 200 OHMs, or just OHMs, upside down horseshoe

Touch one probe to pink wire and Ground the other probe

Should see higher than 1.5ohms, usually around 2 ohms

Under 1 ohms mean motor will draw too many amps and blow the fuse over time

It could be the connector on the top of gas tank is corroded or the pump itself, need to pull bed back or lift it to test further
The ground wire for the pump is also part of this, so it needs to be tested when you have access to top of the gas tank