Looking at the charging circuit diagram, the sole load path that could blow only the No. 15, 80A fuse and no others is the B+ wire from underhood fuse box to alternator. I see several possibilities; 1) an intermittent short somewhere in the B+ wire from underhood fuse box to alternator 2) the battery has an intermittent internal short that somehow causes a high current demand spike on shutdown and blows the fuse w/ high current from the alternator, instead of from the battery. If you have a spare battery, you might try substituting for a while to see if this cures the problem, 3) an intermittent short in alternator field winding, voltage regulator, or rectifier causing Fuse 15 to blow. Possibility 1) may be more likely, but will require opening into the wiring harness to inspect the B+ wire. Try inspecting all the B+ wire you can access first.

This is one of those problems that may require simply substituting parts until you eliminate the fault. I have found that used parts offer a reasonable cost way to do this.

good luck

 

that is a GREAT help thank you Texas.

 

Wow. This is a very informative thread. Be sure to keep us updated! Especially if you figure out what the problem was!

 

well I checked the visible parts of the B+ wire and everything is still intact, IE no charred areas or exposed wire, but I know that there can be a short with all the sheilding still in place. the Battery is only 5 months old, it is a SuperStart Maintenance free battery from O'reilly, the Battery that was previously in there was an AutoCraft Silver from Advance, but that one was in there when I bought the car. will keep you guys updated. just out of curiosity how much would a complete new B+ wire be? and is that something I can get at a parts store.

 

Just a reminder - while you are working on electrical stuff under the hood make sure you ALWAYS take off any rings you are wearing. If you get the ring between a hot wire and ground it'll take your finger right off.

A continuity checker is a useful tool for checking for shorts. For instance, if you can disconnect both ends of the B+ wire and connect one end to the checker and the other probe on the checker to ground, try to manipulate the wire at various places along its length. Gently bending or stretching, shaking etc. If you get any reading on the checker - like around 0..3 ohms - you have a short.

Having said that, considering that your problem only happens when you shut off the engine, it doesn't sound like a mechanical problem. Alternator or regulator sounds more likely.

Rod

 

i am not doubting you...but how will it take your finger off? i am having trouble visualizing that.

 

Just wondering, could the engine shudder/shake at shutdown cause something in the alternator - fuse box circuit to vibrate and short over? I would be curious to take a look at the wiring in the fuse box to see if any are actually able to contact another.

 

smaglik: i am not doubting you...but how will it take your finger off? i am having trouble visualizing that.

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Depends on which wire you come in contact with - but a gold ring (for instance) between B+ and ground will conduct current real well and become red hot very quickly - faster than you can react. The temperature is what does you in and if the ring makes it tored hot, that'senough to take off the finger... so I'm told. A pal of mine *almost* lost his finger that way. Had to take antibiotics, though because the skin under his ring became badly blistered and got infected.

 

well I dont wear any rings so that wont be a concern, also when I work on any car I have a pair of Craftsman Mechanics gloves that I wear. Not sure about the engine shutter considering theres something going on while the car is running that causes the fuse to blow when I shut it off, I know when its going to blow before I cut the car off because from a dead stop when i start to go the whole car will cut out for about a half second then come back to life, then it will run fine until I shut it off and thats when the fuse pops. Its been running fine here recently again and its been raining the past couple of days so I havent been able to check the rest of the wire, but when it stops I'll give that wire test a try.

 

bought a new battery yesterday. got a sear die hard, pulled out of sears parking lot and it did the same thing, had to replace another fuse when I got to the house, so short in the battery eliminated as a possible cause.