I inadvertently left my key in the "RUN" position after performing some diagnostics, I didn't realize it until about 2hrs later and thought maybe I caused some harm but the truck started right up like it always does.

Can any harm be caused by doing such a stupid thing? burn up a coil? burn up a ballast resistor? etc., or is there a "safe guard" in place to prevent such harm?

 

No harm done.....I would think you caused more damage to yerself frettin' about it than any actual electrical damage.

 

lol, I think you're right. I didn't know if my coil would over heat or something worse, I appreciate your input.

 

What year is your truck? Profile sez 2018 F150? Ford went to electronic ignition in '73? But I think you're OK regardless, assuming you're in the correct forum.

If the round type classic coil, used in the earlier contact ignition points system is energized with the engine off (key in RUN) it will overheat and spew oil (and lots of wire too) all over the place. It's ugly. Two hours is probably plenty. If the points happen to be closed, they can get burned up. I'm trying to remember if the operator's manual or shop manual even mentions this. I don't believe so, which is kind of surprising. Electronic modules that replace points, like the Ignitor 1 from Pertronix can get roasted, later versions have a safeguard for this.

 

Yep, if the distributor is in the right (wrong?) position, you can not only fry the ignition coil, but also the Dura Spark ignition module as well. But since yours fired right up, it sounds like you dodged a bullet and you're good to go.
I'm not sure if can damage a resistor wire, but I bet if one is not in perfect shape to begin with, the heat could cause it some distress. But since they're actually made to run hot (it's in their very definition "resistor" after all) and are jacketed to protect the other wires around them, likely they can last under these circumstances as well.

Paul

 

It's a '77 (non-points) I just didn't know if maybe the coil, or ignition module, was being energized this whole time and potentially overheating.

While I am on the topic ….what systems are still getting 12v in the key "RUN" position when the engine is not running?

 

I blew up an Msd blaster coil that way. Left the key on listening to radio while working on stuff. Heard a pop noise, lid blew off coil and blew oil all over.

 

So the coil is energized with the key in "RUN" and the engine not running? Does this only apply to the earlier points ignitions or the latter pointless ignitions as well?

 

'77 with the later electronic ignition. Everything appears to be OK but I am still uncertain if I put any undue stress on the ignitions electrical components i.e. coil and control module.

I will ask this again.....which, if any, of the ignitions electrical components are energized with the key in the "RUN" position but the engine NOT running?

 

1Ton, are you referring to the earlier points ignition, or the later electronic ignitions as well? Tedster, in his reply stated there was a "safeguard" in the later electronic ignitions to prevent such an issue (burning up coil and module).

I am not trying to split hairs here, just seeking clarification on the matter. Thank you.

 

You are way too worried about absolutely nothing. If the truck still started and ran fine, you're good.

 

Well not exactly, Pertronix Ignitor modules, designed as a drop in replacement for contact points, have protection circuitry in the Ignitor II and later series. However this won't prevent the ignition coil from roasting as far as I know.

edit: Yes it should. If the points, or un-protected electronic module is lined up in the distributor just so (closed) it presents a direct and continuous short of the thick, heavy primary windings of the ignition coil.

 

As pretty much all of us have said, if you're running, you're good to go.
I should maybe not have brought up some of the possible scenarios, but I thought it would be good to know that stuff and, well, hey you asked!

So here I am, about to do the same thing again!
Basically, there's nobody, even from the first day these trucks were brand new, that should not have had a spare ignition module sitting in the glove box or under the seat. It's just the nature of being prepared for any eventuality. And electronic and electrical components sometimes do fail. Unfortunately sometimes very often and quickly! So it's nice to be able to get back on the road quickly and without drama or undue stress.
But you can, and people sometimes do, as you've read here, mess up their stuff by leaving the key on. And no, it's not just a points thing. With either type of ignition you either get lucky or you don't. Hence my mentioning the position of the distributor/trigger mechanism.

It can. Just like points ignitions can, but in your case it apparently it did not.

All the usual suspects. When the key is in RUN, your ignition coil and ignition control module DO HAVE POWER GOING TO THEM. It's where the trigger sits that depends on whether that power is simply sitting there waiting for something to happen, or it's actually passing through and building heat.
I used to think it was only on points ignitions, but I've been assured by the experts that write books at least, that if a magnetic trigger wheel (armature or reluctor wheel) is lined up with the magnetic pickup point (stator) it's the same thing as the points being closed. At that point the power is passing through both coil and module and building heat in those components. More so because there is no engine cooling fan or air from movement passing through the engine compartment.

See above. I'm not sure of all the things going on by book learning. I'm not an electrical engineer so have to trust to what I've read in magazine tech articles and from hearing what others say. And about other's experiences, such as hivoltj's and tedster's

But what would you do about it? Just replace them before they fail? I suppose if they were showing signs of stress, such as melted components or not working properly, that would be a good thing. But since they're working at this point, you probably dodged the bullet and are just fine using the existing ones.
In fact, I'd rather use a known-good 40 year old setup than an unknown new (and possibly POS) from an auto parts store.

See above. And re-read Tedster's post because he specifically mentioned the Pertronix Ignitor (an aftermarket points conversion ignition system) when he mentioned later safeguards. Nothing specific about factory stuff.
But yours is not a "later model" in anyone's book anymore anyway. In current and more modern vehicles, yes there are many computer controlled safeguards. But in your version of a "later" vehicle, where we are talking about Dura Spark ignitions, (which is now at least 44 years old, having started in '74 in some vehicles) this no longer applies as a "later model" in most books.
So your ignition is still pretty primitive compared to the new stuff and as far as I know does not have any electronic safeguards.
Heck, maybe it does and all the different things I've read were incorrect and there is no way for a stationary magnetic trigger to allow the coil to be grounded through the module. If that was the case then there is no chance that leaving the key on can overheat things on a factory Dura Spark setup.
But even 40-plus years on, there is still debate as to why there is even a START sensing wire connected to the module. Many say that there is no start-retard function on Dura Sparks. I do know from reading Ford books however, that at least some of the different modules did have that function. Just that nobody has reached a consensus that I've seen that indicates which ones.

But none of that matters anyway, since yours is working just fine.
It could die tomorrow however, and still have nothing to do with you leaving the key on. In that case the sad part is that nobody will ever know if it was due to old age, standard parts failure, or you leaving the key on.
Nature of the type of part.

Paul

 

only if the trigger wheel is lined up with the pickup I believe. That truck was a '78 with all MSD parts Btw. Distributor, ignition box and coil were all msd stuff

 

1Ton, I sincerely appreciate your educated and in-depth reply, along with all the other replies, I appreciate them all. I guess it's just my OCD that makes me question things that most others would consider insignificant lol.

In regards to carrying a spare ICM (ignition control module) I have heard this from many people, my question is....where can one buy an official Motorcraft module, as opposed to the cheap Chinese modules from Napa or Autozone?