Why will my truck only push start and not jump?
Bad connections, battery terminals, ground, switch all possibilities at this point, maybe even a bad battery.
Your starter may have failed.
Also the wire in common jumper cable is too thin to supply 100 amps of current for the starter motor. Cheap jumper cables can recharge a depleted battery but can not substitute a failed battery.
It is not the starter
Clutch safety switch, you can temporarily jump it at the connector with a paper clip or anything similar to test.
My guess from here is that your battery is possibly totally dead and will not accept a charge or the Starter solenoid is not functioning properly if at all. With a volt meter in hand you can answer many of your own questions.
What happens when you turn the key…a click and no start? No noise at all? How are your headlights…do they come on bright? Have you tried to put the truck in neutral and bridge the two terminals on the starter solenoid? We need to know these things and honestly we need the resting batt voltage to begin any accurate diagnosis. Let us know…this shouldn’t be too hard to figure out…not many suspects in the suspect pool here really.
Another possibility is a popped fusible link. No matter the cause, this should not be difficult to sort out.
You are giving us almost nothing to work with. You didn’t even tell us what happens when you try to start it. We need a lot more detail before we can do anything but throw stuff at the wall to see what sticks.
Here is the starting diagram.
Trace the positive battery cable to the starter relay. Pull the wire with the rubber boot off of the relay & jump 12 volts to that pin.
It should crank when you do this so be sure the transmission is in NEUTRAL & the key is turned off. If it cranks when you do this the clutch safety switch is the most likely problem
“It is not the starter.”
So if what you’re saying is, the starter cranks the engine over but the engine won’t start, the problem might be with the Ignition Control Module.
The ICM functions in two modes. These are the start mode and the run mode.
When the ignition switch is turned to the start position to start the engine, the ICM goes to the start mode which allows full battery voltage to the ignition coil to provide a strong spark when the engine is cold. Then once the engine starts, and the ignition switch is allowed to move to run position, the ICM switches over to the run mode. The ICM then cuts the voltage to ignition coil because if this isn’t done, the higher voltage from the charging system would fry secondary ignition components.
So what might be happening is, the ICM has failed in the start mode, but is functioning in the run mode. That may be why the engine starts when the truck is push started with the ignition switch is in the run position.