Alternator batt post red hot

John Dirks Jr

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The problem is with the 92 Lx which has 3G alt upgrade mounted low on Vortech bracket. It has 4ga batt cable, with 200a breaker block, all proper harness plugs. It was a good install that’s been working well for several years. The altat the install time was a new 3g.

Pulled into the car show the other night and a person says, “there’s something glowing under your car”. Got out and looked under and saw the post and main batt cable glowing red hot.

The batt wire insulation is toasted for a length about 3” up the cable from the connection. Regulator wires and ground not showing and signs of heat. Just the positive post and wires connected to it. Checked the full length of remaining cable and wires including everything at the fuse block, starter solenoid and battery. No evidence of over heating anywhere but directly at the back of the alternator. Connections at the alternator were tight and corrosion free.

I’m trying to conclude where the heat started. Was it a wiring connection problem or an internal failure of the alternator itself?

Again, the setup had been performing well for several years including under heavy loads of hot weather with ac and electronic fans and what not

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jrichker

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The alternator is toast, but you already knew that, it probably has an internal short circuit. If you connected both the old alternator power wiring and the 4 gauge wire to the alternator output, that is a big no no. That would be why you didn't blow the fuse or trip the breaker. The 4 gauge wire should be the only wire between the alternator and the battery and should be fused for no more than 120-130 amps.
 
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Mustang5L5

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I concur. I would bet those two #10 wires were overheating and getting that terminal hot. Leave them disconnected and only run the large guage wire. Keep the #10 hooked up on the starter solenoid
 
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John Dirks Jr

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Ok, I’m tracking. Thanks everyone for the help thus far. The alt is toast because it fried the post and I can’t fix that part, that I understand. Why it would have an internal short, I still don’t understand.

Anyway, I’m following the idea that the two #10’s shouldn’t have been connected at the back of the alternator.

Why are there two individual 10’s originally at the back of the alt? What does each one originally do? I understand that you’re telling me not to connect them at the alternator. What do I do with them? Splice together or leave them individually disconnected and isolated?
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John Dirks Jr

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Here’s the fuse block that came with the kit. It’s a 200 amp. So I guess they sent me an over sized fuse?
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John Dirks Jr

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By the way, the 200 amp is not blown. Should it be if there’s a dead short in the alt? I would think so
 

John Dirks Jr

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By the way, the 200 amp is not blown. Should it be if there’s a dead short in the alt? I would think
 

jrichker

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Ok, I’m tracking. Thanks everyone for the help thus far. The alt is toast because it fried the post and I can’t fix that part, that I understand. Why it would have an internal short, I still don’t understand.

Anyway, I’m following the idea that the two #10’s shouldn’t have been connected at the back of the alternator.

Why are there two individual 10’s originally at the back of the alt? What does each one originally do? I understand that you’re telling me not to connect them at the alternator. What do I do with them? Splice together or leave them individually disconnected and isolated?
31DF9475-86AA-417C-872B-54F28C2470D4.jpeg

The 10 gauge wires are only good for 30 amps each, so by using a pair of 10 gauge wires the circuit can handle the 65 amp rating of the stock alternator. Ford would have to use a 6 gauge wire, which was a lot more expensive than 2 pieces of 10 gauge wire.

The maximum size of the 4 gauge fuse or circuit breaker should be 120-135 amps.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The if 4 gauge path is fused for 200 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 260 amps, which far exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.


The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.


http://www.stangnet.com/mustang-forums/threads/3g-alternator-install-a-how-to.646825/#post-6673702

Alternator wiring.

attachments\50374


attachments\52292




If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.
attachments\52294


Starter solenoid wiring 92-93 model cars.
attachments\53216
 
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John Dirks Jr

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Thanks for the help j....I’m on it.

Can anyone tell me how to verify short in alt? Test with ohmmeter between where and where?
 

jrichker

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Set the meter to low Ohms and measure the resistance between the alternator case and what's left of the alternator output stud. A short will measure almost the same as pressing the meter leads together.
 
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John Dirks Jr

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There is no short showing between the batt post and case. None at all. There’s no burn marks or other evidence of super heating inside the alt case. All over heating evidence is at the post, on the cable crimps and a couple inches up the cable.

Is it at all possible that I simply had a very poor connection at the crimp which allowed high resistance to generate that kind of heat?
 

General karthief

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Yes.
Note: this answer is not based on any mechanical experience whatsoever. It is the opinion of someone that should not be fooling around with anything that involves wiring and electrical connections.
 

billison

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When I did my 3g swap I pulled all the wiring out of the loom and completely removed the old charge wire. Then I ran the new wires inside a new loom. No extra wires , no fuss.
 
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John Dirks Jr

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The failure was due to the connection at the alternator stud being loose. One or more of the alternator diodes is blown.
Been there...done that.

How are you sure diodes are bad? If it was a loose connection and that's it, I want to replace the damaged cable and post. the damaged part of the post screws off. Maybe I can find a replacement part. Such as this

https://www.ebay.com/i/332092313242?chn=ps