Hi everyone. I'm having an issue and I'm hoping you guys, with relative ease, can help me diagnose it.
Please bear with me, ill be as specific as I can.

The truck is a 99 Expedition Eddie Bauer with a 5.4 (vin L) and AWD. The issue is that when I try to start the truck (with an original key) "nothing" happens, the truck doesn't even try to start, as if there were no starter, or it had a bad battery.

When I get in, I have interior lights, seats move. When I roll the key to the acc position I can operate the windows, I have dash lights and gauges. *No check engine light*

When I try to start the truck, I can hear the ignition switch under the steering wheel click. I can also confirm that the fuel pump works and fuel pump relay... (I am describing the 1"x1" black, cube shaped item) located in the fuse box under the hood also clicks...appears to be working properly...and has been swapped with a known-working unit and got the same result. So fuel is out.

The battery is new and tests good on all accounts, as is the alternator. The starter relay (this is the 3 terminaled item on the firewall near the battery.) Is also fairly new.

So here's what I know...no crank no start in park or neutral. BUT, if i leave the key on, and use a screw driver to jump the two large posts on the starter relay (on the firewall) the truck will start, idle, and run just fine. The truck will shut off when the key is turned off, no issue there.

I have not checked the headlights in any capacity (dimming during start, if they even work currently.)

I have pulled every fuse under the dash and under the hood, all are good.

Here's where it gets cool. A friend of mine has a power probe tool. When I hooked it up to the battery and tested the starter relay voltage with the key rolled forward I got good voltage off the....bottom? post, I think, and nothing off the top one. I pulled the little wire off the terminal marked "S" and probed the wire, not the terminal, that was giving me approximately 5v. When I applied the power probe tip to the smaller of the three posts (marked "S" and gave it a jolt of power....the starter kicked on, worked as it should, and tried the start the engine.

Given this information gentleman, i dont know how to proceed. All the wires I can see from the battery, starter relay, starter, and alternator appear fine, minimal corrosion, no extra wiggles.

I would like to postulate my own guess in the hopes I might just be right for a change but it seems to me that if I can jump the starter relay, and apply power the small post, and get a reaction from the starter on both, I assume its good.

What I think is that the signal somewhere from key in the ignition, to the starter relay has a fault. The only thing I know of in that system would be the ignition switch itself located under the steering column.

From here, I am open to all questions and inputs. I really appreciate your time, and any help provided. Be well.

 

Not supposed to have the check engine light one in ACCY. Put it in RUN and it should be on.

You didn't indicate whether or not the cluster powers up in RUN.

If the problem is that there is no starter activation in START (sounds like it), check the series circuit of the ignition switch > fuse F21 under the dash > DTR switch > starter relay "S" terminal. Start by check F21. If not blown, use you meter or test light to see if it goes HOT IN START.

 

If applying power to the S terminal on the starter relay causes the relay to turn the starter on, then the issue is power loss on the S terminal wire. Several things could cause this, the starter relay in the fuse box, the ignition switch, or the Digital Transmission Range (DTR) sensor down on the tranny. Have you tried reaching over with your left hand and holding the key in the start position while moving the shifter through all of the gears with your right? If not, try that (foot firmly on the brake) and see if the starter kicks in any gear other than park or neutral.

 

There is no starter relay involved upstream of the big one he already tested at. See circuit description I posted earlier.

Yep, do this.

 

Yep, I see that now, should've checked the diagram first. Anyway, here is the diagram and it looks like if 15A fuse 21 in the central junction box is blown, that solenoid coil wire won't power up.