Electrical Melted Fuse On 3g Alternator Power Wire

Discussion in 'Fox 5.0 Mustang Tech' started by boostfrk, Jul 8, 2013.


  1. boostfrk

    boostfrk Active Member

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    So I installed a 3g alternator with the proper wiring in May 2012. I followed jrichker's write-up, used 4 gauge power wire from the alternator fused with a 150a fuse, and also upgraded my ground wire from the block to frame rail with a 4 gauge piece. Everything has been working flawlessly until yesterday.

    I started the car in the driveway and let it idle for a couple minutes while I ran back inside. Came out, got in the car, started to pull out of the driveway and noticed a little bit of smoke coming from the driver's side of the hood, where the fuse is installed.

    This is what the fuse looks like now.
    [​IMG]

    Did the fuse just fail and I need to replace the fuse and fuse block with a new 150a unit? Is there something else at work here, like a bad ground somewhere? I've looked around and can't find any bad grounds, but this is obviously I huge safety issue so I want to make sure I get this diagnosed and fixed properly.
     
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  2. betke76

    betke76 Member

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    it looks as if you have a bad ground somewhere
     
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  3. MikeH686

    MikeH686 Mine is only two inches though.

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    Are those wires going to the fuse tight?
     
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  4. mikestang63

    mikestang63 Mustang Master

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    I would recheck all of the grounds. Wondering if that fuse housing touched metal and was grounding out by the housing instead of the actual 4g wire?
     
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  5. boostfrk

    boostfrk Active Member

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    They are, at least from what I could tell. The wire on the line side (from the fuse to battery) was obviously charred and melted so it's hard to tell how tight the set screw was. The other one was tight. That was my first thought; loose connections at the fuse block.

    Interesting thought. Wouldn't you think that if the fuse housing had touched the metal against the inner fender that it would have arced and left a burn mark on the metal? I'll re-check all of the grounds, but I went over the main ones quickly today and didn't see anything loose.
     
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  6. MikeH686

    MikeH686 Mine is only two inches though.

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    Bad grounds you would assume it be charred there because of the loose connections but i also think that fuse holder has a plastice casing i thought at least
     
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  7. mikestang63

    mikestang63 Mustang Master

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    I personally do not care for those screw type fuse holders. I prefer to use these water tight mega fuse holders.

    [​IMG]

    What I did was drilled a hole at the bottom of each side of the stock battery tray and ran the 4g wire through those holes. The fuse holder sits nice and secure away from the elements in the little cavity in the bottom of the tray under the battery. The other side of the wire runs to the battery side of the solenoid.
     
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  8. boostfrk

    boostfrk Active Member

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    Can these types of fuse holders be had locally, or do you have to purchase them online?
     
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  9. mikestang63

    mikestang63 Mustang Master

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    NAPA sells them Part # BK 7821143 or Flea Bay. After looking more at that picture I am fairly confident the plastic started to overheat, allowing the connectors to loosen up and that led to the failure. Those type of connectors IMO are meant for stereos and such, not this application..

    One more suggestion. Try and buy the 4g wires with pre crimped eyelets for the connections. Do not try buying the wire and eyelets and crimping them yourself as you will not be able to supply enough clamping pressure. They will eventually loosen and you will have another failure. Most auto parts sell these cables with eyelets on both ends in various lengths. If you do want to make the cables on your own, you must solder all the connections.
     
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  10. boostfrk

    boostfrk Active Member

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    Thanks, I'll see if I can pick one up with a 150 MEGA fuse from Napa.

    I can understand buying a short wire with pre-crimped eyelets for the connection from the fuse to the battery, but the wire that runs from the alternator to the fuse block is probably ~5' long. I'd rather not replace that with a pre-made cable as I imagine it would be pretty expensive. Guess I'll check at Napa though and see what they have.
     
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  11. boostfrk

    boostfrk Active Member

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    Looks like maybe the wire from the alternator to fuse would only be $10 or so, which isn't too bad. I'll probably pick that up and a new wire from the fuse to battery.

    I was re-reading some posts about checking grounds and noticed jrichker mentioning that when you upgrade to a 3G alternator you should run a 4ga ground from the block to the same ground point as the battery/computer ground, right on the inside of the drivers fender.

    Is there a huge advantage to running the ground to this location? I upgraded this ground but ran it from the block to the frame rails; to one of the sway bar mounts specifically. Do I need to move this ground as well? I'm not sure if the cable I currently have is long enough or not.
     
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  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    +1 on the fuse holder. The audio equipment style fuses aren't designed to withstand the temperature under an automobile hood.

    The plastic melts a little because of the under hood temp and then the connections loosen. Loose connections make high resistance which makes more heat. More heat the melts the plastic and the cycle repeats itself until it either catches fire or blows the fuse.
     
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  13. boostfrk

    boostfrk Active Member

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    Fuse holder and 150A MEGA fuse will be picked up from Napa this morning.
     
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  14. boostfrk

    boostfrk Active Member

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    Got everything replaced today, no more smoking :cool:
     
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