Alright so i recently purchased a 1990 f250 4.9 straight 6 engine with manual trans. When i first got it, it needed a jump in order to start..well after a few times that stopped working. I replaced the battery, starter, and solenoid. Still wont crank. You can hear the fuel pump going when you turn the key so i know its not that, im not really sure what else it could be. I jumped the starter just to get it running and back to my house but im really not sure what to do from here. Does anyone have an idea of what the problem could be?

The engine will not crank....as in the starter is not engaging and the engine turning over?

That is correct

Have you checked your cables?....and have you confirmed that the solenoid is energizing?

As Duncan said could be the cables, relay,a bad connection or the starter.

Check ground wire connection. Both ends.

There is a connector on one of the wires for the starter (I forgot if it's the 12v or the ground wire) that is a blade-style connector and it gets loose and kills the start.

Are you saying that when you give the starter 12 volts, it does turn over? You're just not getting power delivery?

Ryan

Starter Switch?? Just because when you turn the key and the pump comes on that its sending 12V to the relay when you turn it to start.

Neutral safety Switch. Could also be bad. or the wiring to it.

See if you have 12V with the key in start at the red and Yellow 12gage wire
at the switch under the dash.

If no its the switch. if you do you need to move to the Clutch same red and yellow striped wire. do same thing do you have 12V in and out of the switch. And then to the Neutral switch on the trans {if it has one] some do and some dont. And then at the relay to see if its the relay or if its a wiring problem.

Look at your clutch pedal. Its got a switch that wont let it start if the clutch isnt pushed. Maybe a bad switch.

I had mine be as simple as the connection on the solenoid, Just needed to be tightened up a bit by using a pair of pliers to crimp down the push on connector.

also i can bypass the solenoid and it will start right up no problem

my thought is clutch switch, try with a jumper on the both cables if that don't work might be in the steering column or the ignition switch

Possibly the same problem

I just purchased the same identical truck except mine is a true junk yard dog. It's been sitting for some time before I towed it home. That said the seller tells me it was slapping the valves off when it last ran. I put a battery charger/starter to it and here is what's going on....1). Gauge lights lit up with ignition on, volt meter reads about 13V,
2) starter (I think) Akers one quick grunt when ignition is turned to start.
3) Checked cables and tapped the solenoid...Same results
4) screw driver to solenoid post, still just a grunt.
4). One thing I have noted is that once I stuck the key in the ignition I can't get it out....

Need to bench check starter next. Truck has been sitting for a long long time. Ideas?

How do you test ignition switch?

You really should start your own post, as people won't realize that you are a new person looking for help on an old thread
That being said, is the motor locked up? have you tried to turn it over by hand?

Is it a manual transmission truck? If so, there is a release you have to push to get the key lock to finish turning back. If it has been sitting along time, it is potentially a stuck motor.