04 Ranger Edge 3.0 4X4 Runs when it wants

So I have a 2004 Ranger Edge, 4X4 3.0, that I have had for almost 3 years. A few weeks ago it decided to not start up. I checked the fuses and even replaced the fuel line relay. No fuses were bad and the replacement did help. I wasn't to sure as to why this happened. I had a diagnostic test ran on it and a local shop, and the only issue they were able to find was the inertia switch had tripped. They reset it and it was running fine.
2 weeks later it wouldn't start after work one day. I tried to just reset the switch myself with no luck. Only thing that helped was the disconnection of the battery, and it fired right up. This happened 3-4 over a two week period. I called the shop back and they said I just needed to replace the switch. I got the part and had it installed, and went to make sure the battery wasn't going out since I never changed it. The battery was bad and needed to be changed out as well. The truck was running great for a week.
It died again, and this time I decided I would take it the local Ford Dealership thinking they new something I couldn't find. The only thing they could tell me was that my coolant reservoir was empty and a flush was needed to be done and it should resolve the issue. I did this, and was able to get home with the truck. It sat in the garage over the weekend unitl I drove around town all day with it yesterday. Got to the last place I was going for the day, and started the truck up. Very weakly it turned on for 5 seconds and then died. Tried to restart it 3-4 times no luck. Again had it towed back to my house this time. After sitting for a few hours I went back out with a code reader hoping it would tell me something. No codes, but 3 tries in it started up again.

At this point I have no idea what it could be. I have thought maybe the alternator is going out. I had a brother suggest the throttle position sensor. One of they guys at a local parts store said it was the ECM. I am at the point where I want to be able to test things before replacing them since I don't have lots of money to keep putting into the truck. So I was hoping that someone out there has ran into similar problems like this and were able to help me. I have a Code Reader and no Codes are showing up.

Welcome to TRS

Yes testing things is a good idea.

You need a volt/ohm meter, $20-$25
They are easy to use

First thing to do is to see if Fuel Pump is coming on when you have a No Start
Easy to do
Roll down the window and turn on the key, you can easily hear the fuel pump run for 2 seconds each time key is turned from off to on, it only runs for 2 seconds, that is normal, you can repeat off/on as many times as you want, it doesn't hurt any thing.
Fuel pump isn't quiet, you will hear the "HUMMMMM"
Do this test when engine is starting so you know what to listen for.

The fuel pump is an electric motor, and once an electric motor starts up it will tend to stay running until it is shut off.
But Starting an electric motor is altogether a different thing, to get the initial rotation started requires more power and that is when you notice a problem with electric motors.
A fuel pump quitting while driving is very uncommon
A fuel pump not starting is common if it is failing
And it can be intermittent and simply sitting for awhile can get it to work again, it cools down or heats up?, or even getting in the truck is enough to vibrate motor enough to start working.
DO NOT replace the fuel pump, test it first by LISTENING for it to start running with key on.

One other test you can do when you have a no start is 50/50 test
Remove large air tube from upper intake
Open throttle and spray gasoline or Quick Start(ether) into the intake
Try to start engine
If it start and dies then fuel flow is the problem
If it still doesn't start then Spark is the problem
50/50


Battery and alternator test
Set Volt meter for DC Volts
Key and engine off, Battery voltage 12.3-12.8volts, under 12.2v is an older weak battery
If voltage is slowly dropping during this test then battery may have internal short, remove 1 battery cable and retest, if voltage is still slowly dropping then battery does have internal short, replace it.
New batteries can do this

Start engine
test battery voltage again, should be above 14volts but under 15volts, 14.3-14.9v is normal
If battery voltage is still in 12volt range then alternator is not "on", could be a fuse or bad alternator
After 5 minutes of engine/alternator running the battery voltage should be down to 13.6v(approx.), under 14volts, if voltage stays higher than 14volts then battery or alternator is at fault, if battery test showed correct voltage with no slow drop then alternator is the problem.

After battery voltage shows 13.6v with engine idling, turn on head lights and heater fan blower to High, voltage should drop then come back up to 13.6v
If voltage stays down close to 13volts then 1 of the 3 Fields in the alternator has failed, not an urgent issue but I would shop for a sale on alternators and replace it within the next few months


Your truck was in an accident and was rebuilt/repaired, that's the only way Inertia switch could have tripped the first time, and it should have been replaced at that time but often isn't.
Once an inertia switch is tripped the first time it never fully resets, a speed bump or even slamming the door can trip it again
So it needed to be replaced

Sorry its been a few days since you posted something, but I did try out some of the things that you suggested with the battery. Started with the battery and alternator test. Battery tested good, tested right where it should have been, prior to turning on. Turned on and it was around 14.5. After the 5 minuets it was still around the 14.5 area. Turned on lights and fan and it never dropped below 14. SO this makes me think its the alternator or its one of those issues where a wire for the alternator is bad and I will be mickey mousing it with some other wire to allow the alternator to charge up.