Alternator batt post red hot

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.

John Dirks Jr said:

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?

Click to expand...

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.







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.


Starter solenoid wiring 92-93 model cars.

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.

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.

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.

A good diode will measure high resistance in one direction and a low resistance in the other when you switch the meter leads around.

See View: https://www.youtube.com/watch?v=hzq2OwTj5ZM