Hello,
I have a 1999 Xlt 3.0l automatic 2WD. It just decided not to start one morning. I took the battery, got it tested it came back good with 12.6V and 547cca. I replaced the starter. I got the old started tested and it was a working starter. I replaced the Ignition control switch under the steering column. The battery cables look good no visible corrosion anywhere. Nothing has worked. When you turn the key on you can hear the fuel pump priming. the Theft light is Not flashing rapidly. all the fuses are good. The relay clicks like it should when you turn the key over to start. The check engine light does stay on after all the other lights turn off. The 2 things I can think of are the Natural Safety Switch but I tried to start it in both park and natural. The other thing I can think of is the computer but I'm not sure this would cause start issues. I have also tried shorting the starter solenoid by bridging the 2 big posts and the starter spins but does not engage the flywheel.

Thank you for anyone who can help.

 

You have a No crank at this time, not a no start :)

Check fuse 24 in cab fuse box, 7.5amp, that fuse activates starter motor

To jump starter motor you need to put 12volts to the smaller "S" post on the starter motor, picture here: https://troubleshootmyvehicle.com/im.../image_T_1.jpg

"S" post will have a smaller wire hooked to it now, unless you missed connecting that back up
Starter has two wires connected, larger battery positive cable and smaller "S"(start) wire that activates it

But you can just use an 18gauge, smaller wire, from battery positive on battery, to "S" Post to activate it, thats what the key is suppose to do

Jumping the two bigger posts will get what you got............starter spins but does not engage so that was correct but not what you wanted
The "S" post activates the solenoid that pushes starter gear out to mesh with ring gear(engine), and THEN it connects the two larger posts together to spin the motor which then spins the engine

CEL(check engine light) should go off AFTER engine starts to spin, because computer "sees" a timing pulse from the crank sensor, nothing to do with starter motor system except that starter is spinning the engine

Computer has no connection start starter motor system, it has no idea anyone wants to start the engine until its "sees" that timing pulse from crank sensor

 

I checked the fuse and it is not blown. None of the fuses are blown. I also switched the relays around and still nothing. Is there a way to bypass the NSS to rule that out?

 

I checked the starter by connecting 12v to the "S" post on the starter solenoid. The truck runs when I have the key on and do this trick. I tested the relay and it works when 12v is applyed to the 85 side. It still does not start while turning the key over. I have replaced the NSS also. I still need help with this headache.

 

Test the base/plug-in for starter relay to see if Key is sending 12volts to slot 85(or 86) when key is turned to START

You can also test if key is sending 12volts to Fuse 24 when turned to START, that fuse has 0 volts until key is turned to START


Ignition switch, in START position(12volts)---------fuse 24-----------neutral switch-------------------starter relay(ground)--------PATS module


Starter relay base should also have full time 12volt slot, slot 30 or 87 should show 12volts all the time, that's the voltage that is sent to "S" post to activate starter motor

slots 30 and 87 are connected together when starter relay is activated by the 12volts from the key, assuming relay is grounded

 

I tested the relay across 85 to 86 and I am getting noting. I also tested fuse 24 and noting when the key is in the crank position. What should I look for next?

 

Ignition switch sends 12volts to fuse 24

 

I replaced the ignition switch and still nothing. Do you think there is a wire loose or Is there a wiring diagram out there somewhere I can trace what wire is not giving 12v?

 

That's not what RonD said to do.

When the Key is turned to Start Slot 85 OR 86 should show 12 volts.

On your test meter, RED wire to slot 85 or 86, Black wire to Ground, with the key turned to start, one of those slots should show 12 volts.

 

Ok, to recap everything. I tested the battery it is good. I replaced the starter, the ignition switch, and the neutral safety switch. fuse 24 is not blown and the relay works when tested. I tested across fuse 24 again and I have 12v going across when the key is in the start position. I tested the relay 85 and 86 like 2011Supercap said to with the positive lead on the multimeter on the relay socket and the black to ground then turning the key to the start. I got nothing when doing this test. I have been driving the truck by turning the key to the on position and bridging the 30 and 87 sockets on the relay. The truck runs and drives good. It just will not start.