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Discussion Starter #1 (Edited)
Fusible Link Repeat Failure (Solved)

The title of this thread is the short story. The long story goes like this.

September of last year the battery light came on while I was on vacation. I took it to a shop and they did some trouble shooting and found that it was the fusible link. There weren't any ford dealerships around to replace the entire cable so they did me a solid and spliced the cable together with battery stud clamps. Finish vacation and get home, replace the splice with an 80 amp AGU fuse and a clear amp-style fuse holder. That repair worked fine until today.

The battery light came on, I checked everything out and replaced the AGU fuse with another 80 amp rated fuse. As soon as I started the car the fuse blew. This time I went through all the wiring, cables plugs, battery clamps and other things that I thought would cause this instant failure. I even opened up the fuse holder and loosened and re-tightened the ends. Since I couldn't find anything else that would cause it I again tried replacing the 80 amp fuse with another.

I know, I know, don't go throwing parts at it if you don't know why something is broken and fix the cause first. I was just thinking, what's another $2?

Which brings me to my question. What the heck would cause a fuse in that specific cable to keep blowing? I don't suspect that the amperage rating of the fuse is the problem since I ran it for over 8 months without difficulty. Albeit, it was wicked hot today and I had the A/C and everything else on, including headlights.

But even when I tried the other two fuses the radio and all accessories were off. Also, I used the defroster plenty in the wintertime.

Any ideas? Could the alternator fail in such a manner that it constantly charges at too high of an amperage? Is there someplace specific that I should be looking for a short that I can't see or would be aware of?

Any and all suggestions please. I've searched the boards for a couple hours today and can't find the recommendation that I need to get this solved.
 

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BACON?
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look for a short in the things that are not fused. like the alternator and the starter.
 

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Old Phart
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Somewhere here I think I saw a note on different wiring where there was a link from the alternator to the starter hot wire....

If this is the case, and the starter main lead had a poor connection (check crimps at each end, some probs. there) extra current could be drawn through that fuse at starting, when you said it blew.

(can't check on mine, different engine plus dark & rain (grin))

Since it didn't blow until starting, it's either getting extra draw then, or shorting only when engine moves.

That gives you a couple more things to look at at least, Good Luck!
 

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Discussion Starter #5 (Edited)
Thanks for all of your input. I'll re-check the connections at the starter, battery and alternator and will look for visible shorts. I also plan to place an ammeter were the fuse would go to see what sort of current is running through there. I figure if I watch the meter both while the engine is running and at start-up that piece of data will best point me in the right direction.

Any other suggestions are welcome since I won't be able to look at the car until after work today.
 

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Discussion Starter #6
another fuse blown

This time it was only a 60 amp fuse and it was in the name of science. SCIENCE!! So I disconnected the cables at the starter and battery and looked them over really well. There was some corrosion but nothing extreme for a 63,000 mile 2003 focus. I reattached the cables and looked over the alternator, the wires inside (i'm failing to remember my electronics training enough to remember if they are brushes or coils at this point) looked a little charred. But I can't really say that they look awful. The alternator is a replacement that went into the car in September of last year. I tried to loosen and re-tighten the bolts for the main power on the alternator but they acted like they were partially siezed. Not wanting to spin them and break any internal connections, or break the red plastic dong that sticks off of the side of it I let them be and just sprayed them with some electronics cleaner.

Then my wife helped me perform the tests. First while the blown fuse was still holding the circuit open I placed an ammeter in its place and watched the readings as my wife started the car. The readings didn't climb out of the meters range (10 amps) until shortly after the car was started. In order to ensure repeatability we tried this a couple of times with similar results.

I also tested the voltage of the battery while she started the car a couple of more times. The voltage stayed at 11v or better and the car cranked smooth and quick.

Then I put my last fuse into the holder. I put my voltmeter across it and watched to see when it would blow. The voltage across it during start up was right around 11v and shortly after startup (probably right around the time the alternator started to charge) the voltage climbed up to around 13.5-14v and held steady while the fuse slowly glowing brighter and brighter until it finally melted and split.

From all of these tests, the only thing that I can deduce is that the voltage regulator on the alternator has failed. Kind of sucks that it is less than 9 months old and has seemingly failed. Also sucks that I really can't test it without removing it from the car. But this is my deduction. Time to go over to my favorite savage yard and see if they will loan me an alternator to test this theory. And buy some more fuses.

I've attached some pictures of what I'm talking about with the ?chared? alternator internals.

Comments, suggestions, opinions? I think I'm on to the right track and will appreciate any further input.

PS: I also plan on calling the shop that put in the alternator to see what kind of warranty they can provide. Problem is it was replaced while we were on vacation and its at least 4 hours away from home. A long drive with no alternator in order to get a warrantied replacement, really.



 

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Old Phart
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Posted via FF MobileHmmmm, somethin`lost in translation possibly..... meter across fuse reading volts should be extremely low reading, those sound like proper battery voltage readings for the events described... Mike B`s been coaching folks lately on how to find a poor connection by reading voltage across what should be a low resistance connection showing little or no volt reading (depending on meter) . for example when one lead is on a battery post, and one on a cable from that terminal - if you get voltage, there`s a poor connection - post to terminal or terminal to wire, so you check each to find the prob. If you show voltage across a fuse, that fuse has a lot of resistance, possibly the cause of the problem?
 

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Discussion Starter #8
You may be right sailor. I may have been overly fixated on watching the fuse blow and missed the tiny m before the V for mili-volts. Either way, I'll be trying a different alternator to see if that relieves the problem.
 

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Old Phart
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Posted via FF Mobile Yeah, that tiny M would make all the difference.... had me puzzzled as it didn`t make sense that it could be happening as described.... you`ve got a good alt. to put out that much current, needs more control though... (grin) harness connectors and pigtail OK? computer control on voltage regulator has done weird things to some when those connections were bad... Just another double check for ya!
 

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Discussion Starter #10
Yeah, I've looked every part of the harness over really well and didn't find anything that looked bad. All connections were shiny and only some green on the wires, nothing major enough to cause a large resistance.

I'm inclined to think its the voltage regulator because the aftermarket alternator didn't come with the extra ducting that the factory alternators have. Could be a large build-up of heat. Also, my parts connections tell me that the alternator is so popular that the aftermarket companies were calling him to get good used alternators because they weren't getting enough cores back. He also said that some of the re-man units only get the brushes replaced and end up getting re-sold with the factory original voltage regulator still in place.

I'll be swapping the alt tonight and replacing the fuse again. It should work. I'll let you know the results.
 

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BACON?
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just for future reference high resistance can not make a fuse blow. only low resistance. the only time corrosion can make a fuse blow is if it shorts two circuits.
 

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Discussion Starter #12 (Edited)
Thanks for all of the replies. I replaced the alternator and replaced the fuse with another 80 amp and tested. There was little to no resistance across the fuse holder, .004 ohms. After the car started, the fuse blew after 15-20 seconds. The reading on the multi-meter was 37-40mV during the failure.

I re-checked the connections and looked for pinch points. I'm second guessing myself now and believe that even if the wire was pinched any place that the fuse would blow immediately and not only when the car was running.

This leads me to believe that the problem doesn't lie with the alternator. This only leads to more questions.

If the starter has a short, would it only present itself when the car is in the on state?

If the battery has a short, would it only present itself when the car is running?

Is there another logical explanation as to why an 80 amp fuse would work in a circuit for 8 months and then not be big enough to compensate for the "normal" running condition?

Does anyone know the typical amperage through that wire? This would tell me at least the minimum fuse that I should need. I have a 150 amp ANL fuse lying around that I can try instead but it costs twice as much as the AGU fuses that I'm using and requires a lot more setup in order to place it in the circuit.

Someone mentioned that the BCM has the voltage regulator and that might be the actual problem. Does this have any credence? Are there other components that I'm not considering because I have tunnel-vision and am only focused on the three components connected to this fusable link?

Could I just re-wire the circuit entirely and run the wire from the alternator to the battery?

I spliced the wire together last year as a temporary fix. What is the real concern with doing that on a permanent basis? What is the fusable portion of the fusable link protecting?

Is there a chance that the first alternator was really bad (I'm going to get it bench tested tomorrow) and that now that the battery is partially drained that the new alternator is just pushing a lot of power (but not too much) trying to charge the battery up?
 

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Old Phart
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Posted via FF MobileCareful with those universal statements, there`s almost always an exception.... Take a corroded fuse for example, it can`t handle the load it was designed for and it`s resistance is a bit higher.... you pick! I`d blame corrosion for that one..... Certainly the proximate cause for failure (grin)
 

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Old Phart
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Posted via FF MobileWell, you`ve got some posers there, may have answered own question along the way. Fusible link is a type of slow-blow fuse in most apps I`ve seen, so direct replacement with a fuse generally doesn`t work. While I don`t know the official output rating for your alternator, it could easily be enough to fry the fuse at max output. System voltage check would be good to determine if there`s an overcharge situation, or variable voltage in the system - either could be from bad regulator internal to alt, or bad connection/broken wires in alternator pigtail connector. (would be easier with a meter that reads the current in that wire, not a practical investment for one job) You did determine it happens while running, so it`s not a starter or "on start up" situation. As to orig lasting 8 mo., may end up writing off to luck if it turns out the issue is high initial charging current because of low battery as you mentioned... Honestly, I`d hook those wires together, or put in a large fuse, just to test system voltage for normal operation, which requires longer (if looking normal) to test than those fuses are giving you...
 

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BACON?
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Posted via FF MobileCareful with those universal statements, there`s almost always an exception.... Take a corroded fuse for example, it can`t handle the load it was designed for and it`s resistance is a bit higher.... you pick! I`d blame corrosion for that one..... Certainly the proximate cause for failure (grin)
what? a fuse only "blows" from heat. heat is caused by current. when Resistance goes up amperage( measure or current) goes down. if the fuse was corroded it would have high resistance and limit the current flow in the circuit.

back on topic

does it blow when you crank it without starting it?
 

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Old Phart
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Posted via FF Mobile Arlen, I`ll take real world experience over theory that says it couldn`t have happened any day. We got off topic when voltage readings reported accidentally didn`t match reality. I had Starter draw questions myself, but OP tested more thoroughly and found a slow blow after running... As opposed to the "when started" in original post... What`s your opinion on fusible link vs. fuse? Actual current would be good to know, but system voltage should be adequate to determine if operating normally, agreed? I forgot to mention Generic fusibles used to be available to crimp into harness, seen any recently?
 

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Old Phart
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Posted via FF Mobile Oh, and BTW, the corroded fuses were a common problem on 70`s and 80`s vintage Honda cycles, not really applicable to this issue...
 

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BACON?
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80 amps is not enough. i know that saab cars use a 125 amp main fuse. replace the 80 with something bigger. at least for testing purposes. then with the cable disconnected check the resistance between the cable and a good ground. it should read OL. that will rule out a damaged cable. since you replaced the alternator i think its safe to say that is not the problem. do you have a picture of exactly how the cable is run? or how is it routed? battery, fuse, to alt then to starter? does the fuse blow if your cabin fan is off?
 

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Old Phart
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Posted via FF MobileThat matches, I was ballparking an 80 amp alternator...
 

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Discussion Starter #20
The wire goes from the battery, to the starter, to the fuse and then terminates at the alternator.

I will test the resistance from either side of the fuse to ground.

I know the factory rating is 175. I've got an ANL 150 that I will put in to test further.

Now that I have the Car Quest alternator out, I will take it to them to have them bench test it and make sure that it was in fact performing within specifications.

Thanks for all of your input. I'll get this.
 
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