Just looking for some feedback to make sure I'm on the correct path.
Truck stalled out on me and wouldn't stay running when I released the key from the start position.
I'm thinking bad ignition switch. What do you guys think? Correct diagnosis?
My lock cylinder has always been loosy goosey. I could pull the key out while it was running.
I don't believe the lock cylinder could be the issue but I ordered a new one with a new switch.
I also ordered a new ICM since I don't have a spare anyway. On the odd chance that might actually be the issue too.
While waiting for the parts, can I jumper the switch connector to rule out anything downstream of the ignition?
On the off chance it could be a bad wire but they all seemed ok and connected.

 

Yes, could be the switch. But it could be the wiring in-between it and the ignition system too.
And yes, you should be able to use a jumper to find out where the power stops, or to get you running again to drive it. You just won't be able to turn it off until you remove the jumper.
In theory, and in practice for some, you're not supposed to leave the jumper on very long because it can overheat or otherwise do some damage to things like coils and modules/ECM's and such. But I've done it successfully for an extended period of time and had no issues.

Do you have a test light, or better yet a volt/ohm meter? This can tell you if you have power to the ignition coil and module when the key is in RUN.
Another test is the pickup in the distributor. You use an ohm-meter to check between the two wires for a reading between 400 and 700 ohms.
You can also test at the back of the switch itself to see if power is coming out of the terminal with the Green w/red wire and Red w/green wires.

And speaking of tests, you can also make sure that the power is coming from the switch at all, by disconnecting the small Brown wire at the starter relay/solenoid and then trying to start it again.
If it still starts while cranking, at least you know the ignition switch is putting out power while it's in START mode. If it does not, then you know the only reason it was even firing when starting is the Brown wire was jumpering 12v to the coil.

Good luck. Definitely good to have a volt-meter handy with these old rigs!

Paul

 

Oh, and I'm just assuming this is the '79 because you're in this forum. But you have an '86 too it looks like, so thought I'd just confirm.

Paul

 

yes sorry it's my 79 f150, forgot I have 2 trucks in the signature. Must remember to specify...
duraspark 2 ignition system
and yes I have both a test light and digital VOM.
I figure I could jumper it, I just never hot started a vehicle before. So I'm not sure which terminals to jump.
Have a wiring diagram but was worried about frying something else.

 

Hah! Yeah, no problem. I think this time it was pretty safe for me to assume. But you know how that goes with our old trucks sometimes!
So best to ask to be sure.

Good luck with getting it started.

Paul

 

With the key in the "run" position you should see 9v at the coil.

If not check the wiring between the coil and the keyswitch for issues.

 

I'm attempting to test my pickup coil. I believe I am doing it right but not getting any reading at all with my DVOM
I'm testing the connector coming out of the distributor.
That looks like this


My understanding is to ohm between the top two and you should get a reading 850 ohms or less than this value by 60 ohms or more.
Also test the bottom and it should show a reading as well.
Putting my test probes on the top two shows nothing, (1 probe on each of the top ones)
putting a probe on the top and one on the bottom displays nothing.
Now maybe it is fried so the results are correct.. I'm doubting myself though because I assume I should see some reading besides 0.
Am I doing it wrong?
Oh and vitaminC did not see 9v at ignition coil, doesn't appear it is getting any power.
I tested with my digital and analog meter. Not trusting my digital very much right now..

 

 

So no voltage to the coil in run is a least A problem. Hopefully you can now narrow down to the source.

Does the truck crank over? Does the starter engage?

If Yes, with the key the "Run" position check for 12v + at the small terminal on your starter solenoid that feeds power to your ignition switch.

If you get a reading of 12v you can run a jumper wire from that terminal to the positive on your coil.
Give that a try. Because if you can get it to run you most likely have an issue with wiring .

If you have no cranking to start or no 12v at the solenoid with the key in the run position you have an issues with your solenoid, ignition, or wiring ☹️
​​​​

 

Don't see a pic, but they're all the same so that should not be a problem for us to figure out. Just look at the wire colors, if the position isn't clear.

I've never actually heard that particular scenario for measuring. I have always read (in Ford service manuals and similar) that you check resistance between the two colored wires (Purple and Orange I think?) and you're looking for between 400 ohms and 700 (or 800?) ohms.
I'm second guessing myself now because I can't remember if the high reading is supposed to be 700 or 800, but it's in the books so I'll find it later.
Basically though, anything outside of that range is bad, and anything inside of that range is good. However, I've always used the theory that if it's close to one or the other extreme, the magnetic pickup should be changed.

Yes, fully open, or zero resistance.
With one probe to the wire connector for the Black w/white wire and the other on the body of the distributor, you should see zero resistance.
I then check to a different ground just to see how well the distributor's body is in contact with the engine block. I've seen where the distributors are not well connected, but then that's why this separate ground is run in the first place. It's connected between the ignition control module and the distributor. But I think having the distributor grounded is still important. I've seen factory modules mounted to plastic, which is not a ground path, so it's possible that the module is simply staying in common ground with the distributor and the distributor still needs to be grounded. I'm not sure obviously...

That's the correct orientation, so maybe your meter is set incorrectly, or you are indeed getting no reading. Which shows a bad pickup coil/stator/thingy.

Not a valid test, so not sure what it's supposed to show in that case. As mentioned above, the third connector is a ground connection. If you look inside you will see how the wire enters the distributor body and immediately attaches to the plate.

Check the meter by touching the two probes together. Should read zero.
What setting do you have it on? Is it an auto-ranging meter (where you just set it to OHMS and it does the rest for you) or do you need to specify a range?

As the others have said, with the key in RUN/ON (does not work in ACC position) you should see 8 to 12 volts at the Red w/green wire on the coil. Does yours still have the stock "horseshoe" style connector where the wires are? One should even be clearly marked "TACH" adjacent to it.
If you do not have any voltage on the positive side with the key ON, as said there is at least a problem. Or likely it is your problem.
No volts, no spark. Simple as that.

If you do the test that Vitamin C mentioned by testing the Brown "I" wire at the starter relay and do see voltage with the key ON, then the break in the circuit is between the connector at the back of the engine and the ignition. A reading at the starter relay tells you that the ignition switch is working and that the wires to the firewall are working. Only the part to the engine has failed.
If you don't see any voltage at the relay with the key on, you'll need to check back at the ignition switch to the firewall area. That is normally where the resistor wire resides, and it could have failed or the switch itself has failed. Or the connection has failed.

Same readings with both? Check the battery directly and compare the readings? Hopefully they're the same exactly, but if they're minimally different from each other at least you know what you're working with.

Paul

 

appreciate your wisdom.
I did some of the tests you provided and wasn't getting anywhere.
Perplexed as to why I couldn't get an OHM reading from my pickup coil I pulled the dist cap off.
Guess what I found?
A broken wire off the pickup coil.. Think that was the problem?
Well I'll find out soon enough..
Off to the parts store to buy a new one..
I can't give anymore REP out but I really am grateful and appreciative for you all taking the time
to share and provide your knowledge!

 

Fixed sort of.. it started up and ran but it sounds like it is off.. I thought I put it back together like I removed it.
Don't think I could have knocked it out of time but I guess its possible from the sounds of it.

 

Absolutely can get knocked out of time. Doesn't take much and even the assemblies themselves can be off even though they're factory made to supposedly tight tolerances. Guess it's hard to harness magnetism in some factories.

I would start by either checking timing, if you have a light, or just twist the dial a bit and advance it a small amount at a time to see if it improves.
If it's idling low, it's almost guaranteed that the timing has retarded during the changeover.

Paul

 

Oh, and as you found out, initial inspections are pretty critical. Might have saved you a week of hair pulling if you'd popped the top right away.
Maybe you would know what you're looking for, or maybe not. But a busted wire is at least old-school still and says what it means. No need for fancy scanners to find one of those!

Anyway, hope it's just timing. I suppose the new part could be bad too. It happens a lot these days.
Did you by any chance also check the ohm readings of the new part? Just as a check of your meter if nothing else, but in this case just to see if it's well within spec.

Good luck.

Paul

 

No I didn't check it yet, it was time to call it an evening. That is my first step though.
My first thought was possibly a bad part. I couldn't find a motorcraft at any of the local parts places.
Rockauto doesn't carry them. So I took the chance with the standard.
I suppose I could have twisted something getting that reluctor off, it didn't fight too hard coming off though.
It is idling low and shaking a bit. If the part ohms out correctly, I'll be checking the timing.