3g Alternator Upgrade

[keithwiggi02]

I recently replaced my stock alternator with the 3G 130 amp kit from LMR and was wondering what sort of change I should expect to see at the dash mounted battery gauge? With the old alternator, the gauge always read low and is what prompted me to upgrade, thinking it was about shot. Though the car never failed to start or presented any electrical problems. With the new alt. the gauge goes to the center at times, but still tends to read lower than I think it should.

I have taken voltage readings with a VOM at the battery both before and after changing alternators. With the engine running and the old alternator, was only reading 12.5 volts. With new alternator, now reading 13.5 volts...still not at 14.5 volts I would expect from a high octane alternator. I don't think its a gauge issue, I notice it changing while I am driving. I look down at times now and it is in the center, something it never did before. But I can also look down and it will be reading low. It also drops when I turn on the lights or heater blower.

The kit was installed with the upgraded 60 wire and went in with no issues. Seems to work better than the old alternator. Was wondering if this a battery issue, something else, or just normal?

 

[mikestang63]

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

 

[keithwiggi02]

This is the kit:

SVE Mustang 130 Amp Alternator 1g to 3g Upgrade (79-85)

It comes with a 4 gauge wire (not 6 as I said earlier} and the fuse block as you described. If you go to this page it includes an installation video which clearly shows reattaching the old wires. The kit even comes with new connectors for these wires, which you say not to reattach. So now I am totally confused... I figured Late Model Restoration knew what they were doing, and I assumed if these wires weren't attached that something wouldn't work.

I believe all of my grounds are good, but I do believe my battery is weak, it is about 3 years old and got drained once by a stuck dome light.

BTW: high octane alternator = colorful metaphor for higher power alt.

 

[jrichker]

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.

 

[OldManRiver]

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.

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.

 

[jrichker]

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.

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.

 

[89oem]

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...

 

[mikestang63]

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.

 

[Shakerhood]

I did not use the black/orange wires either, the fused 4 gauge wire is fine.

 

[keithwiggi02]

It makes perfect sense, I understand electrical theory. I was concerned that something may not get power if those wires are left off. If you have done it this way before with no issues, I will take them off.
I'm also not clear on the additional ground wire. mikestang63 said, "add another 4g ground wire from the block to the 2ndary ground post behind the battery." Is that the engine block he is referring to? Basically you are saying add another 4G ground from the engine block to the car's frame? Again, the LMR instructions said nothing about this.
I can't believe LMR would post installation instructions that are that wrong, and not just wrong, but dangerously wrong.

 

[Shakerhood]

Yes adding an additional Ground is also a good idea.

 

[mikestang63]

It makes perfect sense, I understand electrical theory. I was concerned that something may not get power if those wires are left off. If you have done it this way before with no issues, I will take them off.
I'm also not clear on the additional ground wire. mikestang63 said, "add another 4g ground wire from the block to the 2ndary ground post behind the battery." Is that the engine block he is referring to? Basically you are saying add another 4G ground from the engine block to the car's frame? Again, the LMR instructions said nothing about this.
I can't believe LMR would post installation instructions that are that wrong, and not just wrong, but dangerously wrong.

Forget what LMR says- I buy from them and like them, but they are in business to sell parts. Read it and learn

87-93 130amp Alternator Install How-to | Mustang Forums at StangNet

Yes- add another 4g ground cable. I attach mine to the lower A/C mounting bracket, and then to the ground post behind the battery where the negative pigtail from the battery cable goes to.

 

[keithwiggi02]

Thanks mikestang for posting the link to that thread....Guess I shoulda come here first! If I had, I don't think I would have made the LMR purchase. My mouth dropped when I saw the date of that thread, a thread started by LMR...correct? You may have saved me a whole lot of grief from a smoked wire harness. As I said, I do understand electrical theory, but something like this never even occurred to me when I installed the alternator. I simply trusted the manufacturer/distributor/selling agency/whatever to know what the hell they were talking about in a freaking installation VIDEO no less...

end of rant and thanks again!

 

[keithwiggi02]

Okay, the additional 4G ground is on and the two factory wires are off!

So far, has been an interesting result. After install, I measured battery voltage to be 12.5 engine off, measured at battery terminals with VOM. Engine started, ran great no issues, allowed some time for idle to set and other stuff computer does on battery reconnect. Then I measured batt voltage with engine running and got 13.2-ish with it bouncing around from 13.2 down to as low as 12.98. So I turned the lights on and presto, voltage jumps up to 13.3. Then I turn the heater fan on and voltage goes to 13.44 and is steadier. What is going on? I am encouraged by the voltage increasing with more load, tells me the alternator is putting out some juice.... and the dash gauge is steady also, but slightly below center.

 

[aztecgwynn]

can someone please clarify what to do to the 2 factory wires?

 

[mikestang63]

slow down there partner. The voltage increasing is your alternator working- it is charging your battery as you put more of a load on it.

Hopefully you did not cut them from the original pigtail, but as you had them connected you did.. You should have just tapped into the original stator wire on the original connector and then tape up the original connector.

What to do? Conect them back to the original wires off the pigtail, Wrap the entire pigtail in electrical tape well. and tuck the entire pigtail out of the way. You may need to lengthen the stator wire a bit. That way, you have the original connector in case you ever need to use it.

 

[aztecgwynn]

Thank you for response, alternator charging and I connected it as LMR directed on instructions given.

 

[aztecgwynn]

Now i get what your saying don't attach in 2 power leads from back of alternator tape those off and tuck away. And let that huge cable do all the work. Thank you for heads up now I have to figure out pulley diameter for alternator and I'm set. 3G alternator not charging at idle.

 

[mikestang63]

What pulley is on the alternator. Normally, swap the old 2g pulley back on ts that is smaller. If you have an auto or underdrive pulleys on, then you will need a 1 11/16 or 1 7/8 alt pulley from March or ASP. Apply loctite to the pulley nut.

 

[aztecgwynn]

I currently have crank under drive pulley with cobra water pump pulley, and the original alternator pulley that came with alternator.