91 f150, 4.9l, manual trans.

Truck starts and runs fine, with no electrical issues except for this one.

Zero volts to the third wire (small red) on the starter relay. Again, starts and runs like a champ if I hold an old wrench across the big terminals. I was quick to suspect the ignition switch at the base of the steering column, but not so sure because all positions work as they should, except "start". Plus the power to everything gets cut temporarily with the key in "start", which is what it's supposed to do.

Things worth noting: Alternator puts out 12.5 volts, definitely worth replacing at this point but it's been that way for a while and I don't think it has to do with the starting issue. Also, the PO cut off the harness for the neutral safety switch, and I've driven it that way for 50,000 miles before this issue came up. The key is a little tough to turn SOMETIMES, though not right now. For a few months, every once in a while, truck wouldn't crank the first time I turned the key, but it would the second time. Yesterday it wouldn't crank at all so I started it with a wrench, later it started normally ONE time, now I need the wrench to start it all the time.

So here's my thoughts on the possibilities:
1) Starter switch is bad, or rod is bent
2) Fuse somewhere (no idea where that might be)
3) EGR tube or something melted the small red wire

Your thoughts?

 

Have you actually checked for voltage on the small wire going to the solenoid, or just assume there was no power since it wouldn't work?


If you DO have power on the small wire it's probably a bad solenoid..

You can check the solenoid by jumping from the positive battery terminal to the small stud on the solenoid..

 

I thought that too. Solenoid is good. There is ZERO point zero volts to the small wire with the key in start, so it's not the solenoid.

 

OK, it was just a thought..........You might check the safety switch on the clutch pedal..

 

"Start", power red- Lt blue wire is only function of that aspect of ignition switch. Its possible only that aspect of the switch failed while allowing full function everything else.

Best bet test it right at switch itself, 12v+ power to red- Lt blue wire key in "start" position, if "zero" replace switch.

If power there id next suspect previous work at Neutral safety switch IE; the PO cut off the harness for the neutral safety switch, maybe the hack job done at that point lost connection.
If you don't care if it works, have no interest in fixing/replacing that switch, resorting its function (I know I wouldn't), just be sure both red-Lt blue wires are directly connected to one another at that point. Other wires at that point would not be needed if bypassed.

Test for power key in run position at that point while you're right there, verify makes it to that point uninterrupted.

If so move on and test at fender mounted relay, should have it there now if nothing happen to wire in between.

 

I will bet you that your problem lies here...

This would mean the PO would need to jump two wires together, which I'll bet he did with electrical tape or some other inadequate method and the wires are now corroded as all heck....

 

yup. bad connection at the splice where the NSS was removed

 

Thanks for the replies, gentlemen. I haven't got a chance to look into the problem as I'm sick as a dog and just pulled an all-nighter rebuilding a motor on 36 hours' notice, so right now I'm not really capable of distinguising between a corroded wire and a hole in the ground. For the sake of future forum readers, I will post an update as soon as I get a chance to roll around in the sand and cigarette ashes under my clutch pedal.

 

It's not the neutral safety switch. Found the jump between the two red wires and it checks out.

Looked for damage to the red wire on the relay and didn't find any. Next step is to check out the ignition switch and the harness that goes to it.

And maybe take a day off work so I have some time to fix my own truck instead of fixing other people's, for once. My own vehicle is last prioity but my reputation is beginning to suffer when everyone sees how badly maintained my truck is.