Truck won't start at random times

I have a 1994 Ford Ranger 4x4 single cab with a 3.0 liter V6 and a manual 5 speed transmission. I've been having a few odd electrical problems in the past few months and I just can't quite find the root of it all. The truck runs great, idles smooth, and never skips a beat, however, every so often, could be ten times in a day, could be once every couple days, it just plain won't start. It'll turn over, but the fuel pump does not turn on and I don't believe that it's not getting enough fire. At first, the only way to start it would be to use starting fluid and run it at high RPMs for about ten seconds, and then the fuel pump would turn on. That no longer works to start it. At first, I thought it was just a fuel pump relay, so I went through about 5 of them, each one busted, and that didn't quite solve it. Then I figured the ground wire from the battery may not be quite heavy enough, so I added a 2 gauge ground to it. That solved it for a few days. Then it started happening again, so I had the battery tested, and found that it was bad. That really surprised me because it was a rather heavy duty battery purchased six months ago. I replaced the battery, and believe it or not, that solved the issue for about a week, and no relays were blown. I no longer blow relays, but now whenever the truck won't start, I have to disconnect the hot terminal on the battery and leave it off for about five minutes, then I'll put it back, and it'll run like nothing happened. I'm thinking it's my computer, but I'm hoping someone else has had this issue before and knows how to fix it. Thanks for reading.

Grizzly_bradams said:

......and a manual 5 speed transmission.

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Count your Blessings !! Pushing the Ranger & Popping the clutch is a old time tradition !
All I can think of poor grounds/ breaks on the wiring, would replace the wiring harness(es) since its a 20yr truck-

So the fuel pump doesn't come on for the 2 seconds when key is turned on.

If this is still the case then I would check a few things.

You can test the fuel pump relay using the OBD connector found on drivers side engine bay by firewall.
Look here for diagram of that connector: http://www.therangerstation.com/tech_library/OBD_I.shtml

You will see the Fuel Pump slot in the connector, if key is on and you Ground that slot fuel pump relay should click shut and fuel pump should come on.
The wire to this slot is spliced to the computers Fuel Pump relay Ground.

When you turn on the key the fuel pump relay's coil gets 12volts from EEC(ECU, computer) Relay, these are next to each other in engine Fuse box.
But the fuel pump relay's coil has no Ground so doesn't close, it is Grounded via the computer.
The computer Grounds the fuel pump relay for 2 seconds with key on, then won't ground it again until engine RPMs are above 500, this is a safety feature.

The power for the fuel pump comes from fuel pump fuse in engine fuse box, this has power all the time and runs to pin 30 on fuel pump relay.

When fuel pump relay closes that power is passed to the inertia switch(via pin 87) in the passenger footwell, it could be just under the top of the carpet or behind the top of the kick panel.
Inertia switch is a safety feature, it will cut power to fuel pump if it is jarred, sudden stop or rollover, i.e. an accident.
It has a rest set button at the top
It has 2 connectors, 12volts in from Fuel pump relay from pin 87, and 12volts out to the fuel pump.

You could hook up a test light to the inertia switch and leave it hooked up so you could see if fuel pump power is coming on when it should, if it is then Fuel Pump itself or the wires from inertia switch to fuel pump have a problem.

If you want to check the computer this is a good page to look at: http://www.auto-diagnostics.info/ford_eec_iv

You will see pin 22 is for the fuel pump relay, it would have 12v with key on because power runs thru the coil to that pin, inside the computer is where it is grounded which closes relay.
There are a few Grounds the computer uses so each needs to be a good ground for all systems to work.

If disconnecting the battery and hooking it back up seems to get things running again, I would tend to suspect a corroded connection, you may need to lift up the engine fuse box and have a look and the back side of the connectors.

Also just a quick check that the Ground strap from the engine to the firewall is still there and tight, usually on the back of one of the heads to firewall, that's the main ground for computer and cab in general.
Engine gets the main ground from the battery, but it and trans sit on rubber mounts, so cab needs a good ground, cabs sits on rubber mounts as well so frame also needs a ground strap from engine to frame, fuel pump is often grounded to the frame.

I had the same problem. Turned out to be a faulty ground in the distributor box. I ran a jumper wire and the problem was resolved. Here is a video that led me in the right direction.
https://www.youtube.com/watch?v=hzSyxaZ3WAg
I hope this helps, good luck!