3g Alternator Upgrade

welcome

Stock mustang gauges are terrible for accuracy. Have no clue what a high octane alernator is.

I don't know about that kit, but you need to run at least a 4g power wire directly from the battery with a 125amp inline fuse and add another 4g ground wire from the block to the 2ndary ground post behind the battery. Do NOT reattach the stock 2g power wires to the + stud on the back of the new alt. Only the 1 stator wire should be jumpered to the new 3g. Regarding charging, the 130 amp alt will not see much difference in charging below 1000rpm. Put the additional ground wire on and that should help. That also probably explains the dropping of the gauge when you turn the lights on. THese cars are notorious for that and also the temp gauge going up when you turn the lights on. The gauages all share 1 power wire on the panel with insufficient grounding. Adding another ground wire off the gauge panel will help with that problem,

If the battery was reading was only 12.5 with the car runing then you had problems as 12.7 is the min volts to start a car normally.. What was the reading at the back of the alternator and at the battery. IT should have been higher at the alternator if it was working properly to charge the battery. My guess is the old aternator was not charging the battery sufficiently, usually when the alternator goes, the battery goes at the same time and vice versa.

Go back and check all the grounds to make sure they are all tight, shiny, and clean. ALl the cables are not frayed, split or wearing, The battery sitting cold needs 12.7 volts to start the car. Charge it up if it is low. Make sure the posts are clean and tight. Check the output at the alternator and battery. You should not have voltage drop. If so, do a voltage drop test.

Also, what pulley is on the alt. I recommend you reuse the stock 2g alt pulley as it is smaller than most 3g alt pulley. If you have Underdrive pulleys, that can cause charging issues unless you run an overdrive alt pulley like a 1 11/16 pulley vs the stock 2 3/8

Not everyone understands the fine points about electricity, and LRS is no exception.
LRS didn't go to electronics college, but I did...
I have seen LRS's video, and I will be the first to tell you that it is wrong. Here's why:

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 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which 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.

See Current divider circuits : Divider Circuits And Kirchhoff's Laws - Electronics Textbook for proof.

jrichker said:

Not everyone understands the fine points about electricity, and LRS is no exception.
LRS didn't go to electronics college, but I did...
I have seen LRS's video, and I will be the first to tell you that it is wrong. Here's why:

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 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which 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.

See Current divider circuits : Divider Circuits And Kirchhoff's Laws - Electronics Textbook for proof.

Click to expand...

I don't doubt you one bit,but...why is it that someone like PA Performance whois in the alternator business also tells you to hook up the black/orange in addition to the 4 ga power feed? If it's such a big no-no you would think they would be aware.
Again not doubting your knowledge,but just curious.

OldManRiver said:

I don't doubt you one bit,but...why is it that someone like PA Performance whois in the alternator business also tells you to hook up the black/orange in addition to the 4 ga power feed? If it's such a big no-no you would think they would be aware.
Again not doubting your knowledge,but just curious.

Click to expand...

Maybe their electrical guru went to work for some other company or he didn't get to proof read the text for that tech write-up. Who knows?

Call your local community college and ask to speak to one of the electronics instructors. Ask him about parallel circuits and Kirchhoff's law. Or you can follow the link I posted and read it for yourself.

Good read, and thats how I understood current as well. Ever touch an overloaded wire even after the current is shut off? The shielding is really hot. Imagine that bare wire would burn you....or your car...

It's simple- do NOT connect the two 2G power wires- period.

They are NOT meant to handle the extra amperage of the 3G. Hell, they are a known fire hazard on the 2G alternator.

Look at it this way- forget all the electical theory JR so rightly explained- suppose you blow the 125 amp fuse in the 4G power wire or it shorts out, Where is all of that electricity going to flow. Through your original 2G wiring designed for at best 65 amps, then through your fusible links, then through your main harness, etc.

Make sense now?

Trust me- your car will run fine with just the 4G power wire, Take the other 2 off, Tape them off and tuck them away, Then add the extra 4G ground cable. That is how I've wired at least 4 Fox Body Mustangs, including my current one with zero issues.