1990 F150, 2 wheel drive
1990 5.0 engine
1990 EEC-IV computer
AOD automatic transmission

I'll start with my questions:
1. Where does the red/light blue wire on the starter solenoid physically go? I know functionally it goes back to the ignition switch. I mean does it go to a connector? Which connector? Where?
2. Does Ford label their connectors? As in, looking at the green connector, how does that translate to the connector labels shown on wiring diagrams?
3. Should the START terminal #3 on the TFI only be hot when the ignition switch is in start, or should it be hot at both run and start?
4. Where is connector C113 and what color is it?

So here's the long description. I bought this non-running truck as a project for my sons and I, but they quickly lost interest. I pulled the engine and transmission and completely rebuilt the engine. Everything is put back together and I'm trying to get it running so that I can get it titled in my name (needs to pass an inspection).

Previous owner or previous previous owner cut the red/light blue wire at the solenoid, spliced a wire to that that runs into the cab to a push-button switch, then back into the engine bay to the always hot terminal on the solenoid. Push the button, engine turns over but turn the key and nothing happens. I've had the engine running but its a hard start and rough idle. Since then and lots of forum surfing I've discovered the ignition coil was connected in reverse and also that the EEC-IV disables the SPOUT during a start and uses the base ignition (which I think I have set correctly at 10 degree BTDC). So I figured the rough start is due to the computer adjusting the timing and not using the base timing and the rough running is due to the ignition coil being reversed.

I've traced the red/light blue wire from the ignition switch connector (the ST terminal) to the lower driver side of the round firewall feed thru connector, then to the green connector in the engine bay (is the green connector C103?). At the green connector there are two red/light blue wires on the male side and one red/light blue and one white/pink on the female connector. There's a gray connector in the engine bay (is that connector C113?) further upstream by my thinking. It also has a red/light blue wire and from the connector leads to the engine loom (the bundle of wires that goes to the ignition coil/TAD/TAB/EGR solenoids, distributor TFI, fuel injectors, then on the passenger side eventually to the alternator). See below, I found this in other posts and deleted the sections I don't have.


The first problem is I'm not seeing the remnants of the wire that was spliced at the starter solenoid. Should it come from the engine wire loom? Or should it run from the driver side connectors, up past the wiper motor, then over to the passenger side and the solenoid?

For the next problem see below, it occurs with the ignition switch mounted on the column and using the key, switch loosened at the column and slide back and forth by hand, and switch disconnected from the column and using a screw driver to move the shuttle back and forth. When I probe terminal 3 on the TFI, it's hot at both run or start. That's the red/light blue wire at the TFI connector. I get continuity from the ST terminal on the ignition switch connector to terminal 3, which should be correct by the previous diagram. If I hook everything up except the TFI connector, I get 11.9 volts at terminal 3 during run and 12.4 volts during start. Putting the transmission in reverse interrupts the voltage. According to the previous diagram that's possible, if the wire at the lower right is shorted or connector C113 is screwy or the computer is back feeding it at the purple/yellow wire, correct? Or am I measuring a stray voltage that is back-fed thru the 22k ohm resistor and it wouldn't drive enough current to trip the solenoid?


I'm really flummoxed at this point. My plan was to splice wires such that the push button switch is placed between the green and gray connector, on the red/light blue wire, so that you'd have to turn the key and push the button to start the engine, but I didn't get that far today. And honestly just getting the key to work would be great. I don't get a signal at my shop either so I do what I can, then come home and look things up.

Thank you!

 

The 1990 EVTM will show harness locations
That light blue with red start wire, splices in at least 3 places (connectors and jumpers)
I have a 1990 EVTM if I can find it (I'm moving)
There should be a jumper for the clutch interlock because yours is an automatic
That jumper will be above the driver's feet somewhere if present
Your 1990 AOD should have a conventional neutral safety switch on the side of the trans, the wires go through it too
That generic Ford diagram is good, but the EVTM will say more about the circuit
Notice the right side (2) connectors with no numbers (between the clutch interlock and the neutral safety switch

 

Thank you, this seems to be exactly what I need! By chance can you send me the 1990 EVTM? I found the 1989 EVTM online but it shows a black connector when I know for certain that on my truck it's a green connector. There must have been a change between the two years.

 

If I can find my 1990 EVTM, I'll post a few pictures

 

Interesting topic!
I have the same issue with my 1989 F150 and have been chasing that exact same problem for hours and hours lol
Truck drove in fine but now NO POWER to starter relay 'hot wire'
Traced just about every wire and resitor down, dash out, replaced A/T nuetral safety switch, Ignition barrel, relays etc. etc.
I know there is an answer? lol Just still hunting......

 

I was able to trace the red/light blue solenoid wire, it's in the bundle on the driver's side, under the air filter box, then to the headlights, across the engine bay to the passenger side, then pops out by the starter solenoid. I connected that wire to the starter solenoid and it now cranks with the key....

....but still doesn't start. I put a spark plug tester directly on the ignition coil then to ground, it flashes once or twice when first cranking and then nothing. I got distracted and left the ignition at RUN and after a while started smelling something burning. The ignition coil was very hot! I had installed a new distributor when I rebuilt the engine, made of Chinesium, and I'm currently looking up how to bench test the TFI.

BTW google "archive org 1989 f150 evtm" and you can download the 1989 EVTM for free, very helpful!

 

Check to see if the rotor is turning
If you are getting only one spark each time you crank it
Generally, that means the roll pin holding the gear on the distributor has sheared, especially with the China distributor
They generally use a hard metal pin, and not a roll pin, in those China distributors, and they break

 

I think it was the TFI, I replaced it with the old original TFI and I'm getting spark now. Still no start, so I can't set the timing, but progress. I'll check the rotor though, that makes sense. I am getting a PIP signal at least.