Hello all,
I (think) I posted this question a while ago when I last had this issue (almost a year ago), but cannot seem to find it up update and am a long-time lurker and (2nd?) time poster of this site, so unfamiliar with the back end..

Anyways, twice now, about a 1year apart, I've experienced a COMPLETE loss of electrical power and am beyond stumped! I've read every forum thread I can google and nothing quite helps..

Truck: 2001 Excursion 7.3, no real electrical mods (DP tuner, brake controller..)
At no apparent cause, (First time I thought it was rain, 2nd time, this past friday it was dry but rained the day before.) Without warrant I will go to start it up and there is nothing, I mean NOTHING. No dome lights even! Batteries are great, connections good, and its perfect (electrically) 99.99% of the time.

After waiting a hour or overnight, it seems to solve itself and is fine again. Obviously my trust is GONE, and I need a resolution or a new truck. Ford dealer service was useless, although thats no surprise...

Last time it did this (in my driveway luckily!) I verified 12.6v at the batteries and 12.6V getting to the engine compartment fuse box (not an 02+, so the little box junction that corrodes away on the wheel arch I do not have, verified this..)
I checked most of the fuses and they were getting power...

Starter relay had 12.6V and oddly enough (to me) 6.3V on the opposite terminal of it, this normal?

Either way, I am going to go crazy trying to guess my way to a solution, truck is back to normal now and acts like it never happened.

TO not leave out any information, this last time I had JUST installed a new CPS, due to it dying on the road, which is super unusual. I had an International CPS and just put the (original?) grey one back in. But I can't see ANY relation to CPS and dome lights / EVERYthing loosing power. Wiring diagrams all show these "ALWAYS HOT" regions, I have to laugh at that now... Not ALWAYS HOT!!

I appreciate anyone dropping some insight, it means a lot.

Addt'l point, when symptom is exhibited, I do mean NOTHING for power. Such like the batteries are disconnected... Not sure of any circuits are time-reseting but it resolved itself in 1-20 hours.

Thanks

 

Yes.

There are no circuits in the truck that are intended to behave that way.

Was this while the truck was in 'failure mode' or after it recovered?

 

I have not heard of a 'failure mode', but Im sitting it it right now and its such as it never happened, the only evidence is that my clock was off.

I wanted to check the fusible links (if they were simple to find) since they are a central power region, but a fuse can't un-blow in time, so that seems like fruitless plan.

No check engine light either.

 

"Failure mode" is when it doesn't work as you described. If you're checking all these voltages when it DOES work, everything will be normal and you're just passing time without doing anything useful.

In the presence of a (VERY) intermittent issue, you have to analyze what all might fail that would account for the totality of the observations, then focus on the elements that are common to that total set of details.

Here are your common circuit elements that can cause a COMPLETE loss of power to the vehicle:

Note: I can't recall the specific routing of the cables off-hand and I don;t have my truck handy to look at. The primary cabling might vary slightly between the battery, starter, and relay. If someone has the specifics for the OP's truck and can chime in, it would be appreciated.

Battery (ies, if diesel as yours is)
Battery negative connection and cable to vehicle ground
Battery positive connection and cables to the starter relay and to the starter motor.

The cable segment to the starter motor is only used during cranking, it cannot cause the rest of the vehicle to go dead.

At the starter relay (ALWAYS HOT connection) is the main cable back to the battery and another set of wires. Those are two gray fusible links in parallel. They're then spliced into a heavier cable inside the harness nearby. That heavier cable then goes to the battery junction box (fusebox) where ALL of the rest of the vehicle gets its power.

The good news is that, if it ever fails solidly, it will be easy to find and repair. The bad news is that it probably won't cooperate with your schedule. BTW, if it's too much of a challenge, feel free to drop it off at my house along with the keys and the signed title :evil grin: and I'll take care of it from there.

In the absence of it cooperating to your convenience, pull each of those connections and clean and inspect them. Check the connection into the BJB, look for any evidence of overheating or corrosion.

 

I was lucky enough to be able to test with my DMM in the driveway upon last failure, I know its near impossible to find an issue that isn't happening. Such is the tireless art of fixing electrical gremlins... :/

If this keeps up I will have to offload it, as sad as that is.. Can't have a vehicle that doesn't work, at its own will; and cannot be fixed (with any amount of relative ease).

That I wish, I traced power to the engine compartment junction box and its input terminal (and many fuses) were getting healthy voltage, yet still no basics such as headlights, or any signs of life.. The fact that it suddenly (upon waiting) decides to be perfect; has my diagnosis mind going nuts! If not for the $, whats the address? lol! (I hate persistent problems)

So it was clean here, no signs of deterioration. It was originally from Arizona, so not terrible.. Since fuses in the box were getting power, how in the world does the basic electrical circuits not work?

I will go ahead and check the grounds, as its a safe assumption to check; but my logical mind says a bad ground wouldn't get "good" due to sitting a few hours.

Lastly, if it helps diagnosis;
the first time this happened, I:
Drove in hard rain, sat a few hours (off) in a driveway;
Began to 'try' and start: all lights on, gp's etc. upon trying to crank EVERYthing went out. (Didn't even engage starter, just lights out)
Successive attempts (waiting a few mins, the power would restore) were met with less hope, even putting the key in would kill everything..

This past time; I didn't even get that far, I opened the door and the dome lights were out. Key in, and not even a chime... Wait and hour and its back in business..


In attempt to clarify; I hope I have not muddied the waters!

I really appreciate the assistance!

 

I had a similar issue. I was racking my brain then a friend of mine who does a lot of work on electronics, both professionally and at home, couldn't figure it out so we tried a hard reboot, aka disconnected both batteries for about 10 mins, and after we re hooked the batteries everything worked fine. I have had no more troubles since. Don't know if it will help but it is cheap and worth a try.

 

That suggests that yours was a simple case of "dirty" battery post connections.

 

Then your logical mind should also say that the same cannot happen with a power line. Yet, you have an intermittent open in the circuit (which encompasses both the power AND the ground paths. Therefore, you know it's happening somewhere.

Those are all symptoms consistent with a portion of the circuit opening up under load due to excessive resistance. When the faulty area cools back down, continuity can be restored.

I go back to your original statement that NOTHING worked when it failed and that is the basis for my analysis. For NOTHING to work yet there is power at multiple fuses, that means only that the open circuit had not yet been encountered or there was a measurement technique used that you you haven't told us about, ie, specific point of connection for the negative meter lead. If you were simply clipped to a convenient spot on the body or engine is not necessarily the same as connecting directly to the post of the battery.

See why it is so critical that grounds, as well as the power feeds, be investigated?

Now, if you want to load up the shotgun (both barrels) and pull the trigger(s), replacing the battery cables would be a logical thing to do. I don't often suggest replacing parts unless there is concrete evidence they are defective, but the intermittent nature of your truck's issue suggests that such measures might be prudent in your case.

 

I value your time to help me out greatly! I am having a heck of a time!

It just gave up on me today again. I drove it to work today and all was well, this afternoon headed out the the library to study and there was no issues. Walking away from my truck, I realized the remote key fob to lock it did nothing, so right then it must have quit. No dome lights, etc.

This is inconsistent with my previous (and your further technical clarification) that a load interrupted the circuit.. I think the heat / cool explanation is perfect, yet now, might not apply to me..

Anyways I went to study figuring a couple hours would let it resolve. Nope! Had to get a ride home!

I'm going to swing by tonight and see if it has life again, it has never failed while running so I could get it home or to a mechanic..

Speaking of batteries, I suspected defective batteries the first time this arose, since Ford Service was useless, I figured pro-rated Interstates could be had pretty cheap as the other set was near new. So anyways this is my 2nd set of Interstate Megatrons and they can't (shouldn't? ha) be defective.

I am thinking I should drop off to a shop and get their opinion, or more importantly just get some new battery cables and ground cables installed. Possibly the fusible links are partially blown, or some weird anomaly.

In reference to my metering, I used as a ground, the battery terminal, the negative terminal "clamp" and the fender ground that the wiper motor shares.. My electrical knowledge is not great though, so I wish I could offer a higher degree of technical knowledge there!

I hate to use a shop as I mostly do my own work, but I just need it fixed now! Plus somebody else to bear the 'gremlin distress'.

FWIW, I like the battery disconnect idea, its cheap and can't hurt! But now as it stands; if it works, I'm not sure I can afford to power it down! ha.

 

You would think so but posts were clean as I had put a brand new positive cable on a month prior. The best I could figure is my aftermarket alarm had issues with the computer. Either way it ended not costing me anything but time and frustration. I hope the OP finds out what it is.

 

Implausible since neither the computer nor any aftermarket alarm can kill all power to the entire vehicle. Only a circuit fault (open) in the primary battery cabling can do that.

 

Things to observe next time:

* does horn work
* do headlights work
* do brake lights work

These are unrelated to ignition key position.
The interior dome lights are also, but gather more data points. Rain on the PCM does strange things.

 

Perhaps I misspoke I meant the anti theft(brain fart can't remember the name). Sorry if I confused the OP or caused any discontent.

 

Update: sorry for the couple days of radio silence.
I waited overnight (sunday night mon-morning) and it still was as dead as could be. Absolute no power to anything.

I decided other than waiting for it to maybe resolve itself in the day, I had it towed to a mechanic (so hard to watch (tear) so I didn't stick around lol) Anyways, I stopped by the shop to give them details, and what do you know, it starts right up (has power, more specifically). So waiting (a long time, at worst) fixes it.

What I learned so far: the mechanic is less inhibited and gave my battery terminal a good physical shakedown and they weren't all that tight. :0 So other than that, they are thinking possible PCM oddities (he tells me PCM controls even the most basic lights) which surprises me.

I am hoping new terminal connectors, or cables altogether is a solution. I believe the truck is 'done' or they are waiting for issue to resurface... I am just happy its not (entirely) my problem at the moment.

Update will follow, might be picking it up soon.

 

That would surprise anyone who can read schematics. Sounds like he doesn't...