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So I'm driving along at night and all of a sudden everything goes black. The headlights and dash lights go out, the ignition stops firing, absolutely no electrical at all, so I coast to a stop. I open the hood and I am looking around on the passenger side of the engine compartment and right behind the passenger side battery I grab the wiring harness that comes out of the alternator, lift it up, and all the electric comes on again. This has happened three times. My next task is to take the harness cover off the wiring going to the alternator and look at each wire to see if there's a short or break, check the connections into the alternator, etc. I have just never run into anything that mimics taking the batteries out of the truck before.
I grab the wiring harness that comes out of the alternator, lift it up, and all the electric comes on again. This has happened three times.
I have just never run into anything that mimics taking the batteries out of the truck
Does this alternator harness run directly to the battery? If so, the fault may be in the crimped terminal at the battery post. When you moved the harness, it affected the marginal connection at the battery.
Do you have this style of battery terminal?::
Those blasted things are notorious for being intermittent.
On page 15 you can see the starter relay(solenoid) and how that is the main power connection. You can also see the alternator a little below that, and how it has several splices out in the area where you are grabbing wires. Unwrapping all that is a good start to find out what the problem is. A testlight might be a good thing to have also to poke the wiring and then wiggle the wiring while watching the testlight.
If I were you I'd first check the battery terminals like kr98664 recommended.
On my truck, my positive terminal was pretty shabby, which caused the battery connection to bounce on and off when the system drew a lot of power. This resulted in crappy cold starts, starter solenoid grinding, and, eventually, a total failure to start the engine when I was in a parking lot away from home. I replaced the terminal for about 3 bucks and some splicing and now it starts up on one or two cranks every time, even when cold.
If this doesn't solve it, you may need to go more in-depth and poke around in the rest of your wiring. But why spend all that time before checking if it's a cheap and easy battery terminal?
On page 15 you can see the starter relay(solenoid) and how that is the main power connection.
So I gets to thinking some more...
Can you please post a picture showing the following?:
1) The big wire on the back of the alternator
2) The other end of this big wire
3) The fender-mounted starter relay
4) The fat cable between the starter relay and the (+) battery terminal
One big picture showing the general arrangement of all these items would be perfect.
I'm not sure my previous answer would explain a loss of ignition AND the lights. I hate to admit it, but I may have been less correct than usual. A picture showing everything listed above would help determine how a single fault could take out all electrical, including killing the engine.
On page 15 you can see the starter relay(solenoid) and how that is the main power connection. You can also see the alternator a little below that, and how it has several splices out in the area where you are grabbing wires. Unwrapping all that is a good start to find out what the problem is. A testlight might be a good thing to have also to poke the wiring and then wiggle the wiring while watching the testlight.
i should have mentioned that my truck is a F250 diesel with twin batteries. Battery terminals all look and feel solid. I've checked both battery ground connections to ensure they are solid. Both batteries are less than a year old. I'll post a picture later today if I don't find anything.
i should have mentioned that my truck is a F250 diesel with twin batteries. Battery terminals all look and feel solid. I've checked both battery ground connections to ensure they are solid. Both batteries are less than a year old. I'll post a picture later today if I don't find anything.
Pictures attached. I will unwrap the wiring from the alternator and double check the integrity of the battery grounds this afternoon.
Thanks for the pics. Wasn't quite the slam-dunk I was hoping for, but now I realize the diesel power distribution is quite a bit different from the gas version.
When the engine quit, I think it was due to the loss of power to that solenoid. Supply power there, the solenoid opens, and fuel will flow.
Since you lost all lights and the engine quit, I was looking for some common point affecting direct power from the battery for the lighting system, and key-switched power to the fuel shutoff solenoid.
What had me second guessing myself is the alternator output. I second guessed that even with the battery out of the picture, output from the alternator should have continued to supply the fuel shutoff solenoid. But now I'm not entirely sure what would happen to the alternator output if a battery cable came loose, for example. The wiring diagram shows an internally regulated alternator, and I just don't know how it would behave.
1) If an external fault (a loose battery cable, for example) was capable of knocking out the alternator output, then that external fault (whatever it may be) is your primary culprit.
2) If an external fault does NOT kill the alternator output, then you'd need to find a common point affecting both circuits.
In the real world? Unless somebody more knowledgeable can chime in, we don't really know how an external fault will affect an internally regulated alternator. I need to highly stress NOT to attempt to find out by disconnecting the battery cable with the engine running. This can cause damaging voltage spikes. So on a practical level, without knowing which scenario is really true, I think you'd have to just physically inspect the wiring and then check continuity end to end for each wire or cable while shaking that harness.
I'm still leaning towards a problem with the smaller cable branching off from the (+) battery terminal. I'd specifically give that one a good shake with the engine off but headlights on, and see if you get any flickering. It looks like that heat-shrink is adhesive lined, so the cable may feel solid enough just pulling on it, but the crimped portion may be flexing enough to break contact.
I think it is more than just the fuel shut-off, since he lost headlights also.
You can see in the diesel diagram link you had in your post, Charge & Power Distribution - Diesel Engines - ???Gary's Garagemahal the starter relay is still a main point of power distribution. But there is a yellow wire downstream that hooks to a splice at the alternator (s202) and if that splice was bad, he would lose battery power and alternator power to the ignition switch and the headlights. If you follow the wire to the right side of the diagram from splice 202, it hits splice 101 which feeds two fusible links, one which feeds the ignition switch and all that stuff (the yellow wire going into the cab) and a black/orange which supplies power separately to the headlight switch for the headlights.
If you go to page 23 in the same diesel link, it says splice 202 is near fusible link J. If you go to page 24 in the same link, in the box to the right it locates fusible link J and U
Thanks for the Suggestions. Trying to find the common point for the loss of ignition and peripheral electrics was really stumping me. I didn't have a chance to get to it today but I should tomorrow. I will work my way through the suggestions offered by KR98664 and Franklin 2, in addition to just generally inspecting all the wiring and connections in that area. I will come back in a day or two if I find anything definitive.
Found the problem...probably. You know how it is with electrical issues. Time will tell if this was the entire problem.
Flipped this connector over to look at the underside and found this. Wiggling the green wire caused the electrical to flicker and every once in a while to completely go out.
Had to cut the connector apart because the halves were fused.
Crimp spliced them for a short-term fix. With this in place manipulation of the wires no caused flickering or loss of power.
The diagram is a bit confusing. C131 has two wires, but the two wires are drawn separately towards the right on page 21.
C131 is the best guess. Both the 10 and 18 ga wires come out of the alternator harness. The 18 ga wire continues into the harness on the left of figure 3 as a yellow with red stripe wire. The 10 ga yellow wire goes to to a splice immediately followed by two fusible links, I think L and M. The wires to the links looked red and black, but they could have been dark green and orange and old and dirty. I can see how a break in continuity would turn the instrument panel and lights dark, but not how it shuts down the ignition and the starter relay. That's what I hate about this kind of problem. I'll only know if it's fixed if the truck does not die for the next 3 months. Right now, she's runnin' good!
