got a 92 diesel,went to start it this morning and wont fire,ran good yesterday,was priming the lift pump but hasnt any resistance on the lever,is the lift punp shot? or ?

 

The lift pump runs on a cam so the motor needs to be in the right spot for the lift pump to have resistance and work.
Try bumping over the motor and try the LP again.

I would check the wire to the FSS and make sure it is not loose.

 

bumped up the motor,still no resistance on the pump lever,cleaned all the connections to the injector pump,still no start

 

Is it possible that the FFS switch stopped working?

 

Yes the FSS can die.
I would try running a hot 12V jumper wire to the FSS from the battery and trying to start it normally.

If that doesn't work, then try this. If it is an auto leave it in Park, If standard leave it in neutral with the e-brake on and wheels chocked, cross the starter terminals with a jumper wire while the FSS has 12V power to it.

If that works you know the FSS is good, but some other bit of wiring is bad.

 

I should have mentioned earlier,the motor turns over but doesnt start,the starter works ok

 

I proof read my post and edit so it was worded better.
Give that a try and start working out what works and what does not to find the parts that is bad.

 

Sounds like the pump's up to pressure. If there's no flow, it'll feel like "nothing".
Odds are good he FSS took a crap, or the wiring to it. The power for the FSS, the A21 circuit I believe, goes all over the truck, powering the coil of the manifold heater relays, the FSS, the VSS, the automatic transmission OD solenoid, etc. A short anywhere will take the whole circuit out. It has no protective fuses except a fusible link, and the ignition switch, which will sometimes burn out to protect the fusible link.

Turn the key on. Check the terminal on the FSS for 12V. If there then the FSS is likely shot. If not, go find the fault in the power circuit.