# Alternator advice?



## Chazz (Mar 8, 2010)

I bought a Classic Update harness kit from American Autowire to completely replace the old nasty wiring in my '67 GTO. I don't know squat about electronics or wiring, so it's been fun learning how to do it all.

I'm at the point where I'm installing the engine harness, and maybe I'm just slow on the uptake but I'm just not getting the alternator/battery/starter wiring. First off, here's the instructions and my current alternator:


























No mention of the battery.....and maybe this is a "duh" thing, but I'm just assuming the positive cable ALWAYS goes to the battery (BAT) lug on the starter, correct? So judging by the diagram, the battery throws power to the starter, which will then transfer power to the alternator (also connected to the battery lug), right?
The old harness had some confusing splicing going on, and I think there was a wire going from the positive battery cable straight to the alternator (the positive cable has a small secondary wire coming off the side: click here for picture), and from the alternator there were a couple wires that appeared to go to this box on the firewall. Is that the voltage regulator?

Next, the original two-wire plug differs from the one provided by American Autowire:








(original on the left, new one on the right)

What am I missing? (other than the empty slot on the new one, as I haven't installed that wire yet haha)


Lastly (and this really determines where I go from here), I think I should upgrade to a higher output alternator, as I've had apparent power supply issues in the past and I do plan on installing a new audio system (and who knows, maybe other stuff like an electric fuel pump etc). But with as confused as I am already with the wiring, I'm lost as to what I should be looking for. I'd prefer to not have to change mounting brackets or do any custom work to install a new alternator, and I'd only like to do this once so I'm looking for one with a good output - maybe 120-140? Or is that just overkill?
And what's the deal with the "one-wire capable" alternators? I assume less wiring is better, but how does that translate to my current wiring situation? And internal vs external regulators? I assume internal is better....



So in short, I'd like to confirm that I'm routing the battery/starter/alternator wiring correctly (jesus, I don't want to fry anything), and I'd like some advice on what kind of new alternator I should be looking for. Thanks in advance!


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## jmt455 (Mar 26, 2012)

Let's see if I can help you out with some of these questions...

*"I'm just assuming the positive cable ALWAYS goes to the battery (BAT) lug on the starter, correct?"*
Yes, connect the red battery cable from the Positive battery terminal to the large "Bat" terminal on the solenoid.



*"So judging by the diagram, the battery throws power to the starter, which will then transfer power to the alternator (also connected to the battery lug), right?"*
Yes, battery voltage is provided to the starter at the large "Bat" terminal on the solenoid. Actually, when the engine is running the alternator will charge the battery and provide power to the vehicle electrical system through the common connection on the solenoid "BAT" terminal.




*"The old harness had some confusing splicing going on, and I think there was a wire going from the positive battery cable straight to the alternator (the positive cable has a small secondary wire coming off the side: click here for picture)"*

You will frequently find a wire from the alternator to the battery, but your wiring diagram shows how it should be done; the alternator output wire has a fusible link in it (the short blue section of wire at the end of the red alternator output wire) at the "BAT" terminal on the solenoid. The fusible link is a kind of "slow-blow" inline fuse that protects the wiring system and components from excessive current; it will melt before the wiring is damaged.

You can use the small second wire on the positive battery cable to provide unfused power for additional circuits, but ALWAYS use appropriate inline fuses or add a fuse block for these circuits when you add them.




*"from the alternator there were a couple wires that appeared to go to this box on the firewall. Is that the voltage regulator?"
*
Yes, the picture shows the voltage regulator mounted on the firewall.




*"Next, the original two-wire plug differs from the one provided by American Autowireoriginal on the left, new one on the right)

What am I missing? (other than the empty slot on the new one, as I haven't installed that wire yet haha)"*

Your AA kit came with a plug for an internally regulated alternator. If you are going to keep your current setup (externally regulated), you'll need to follow the directions in the kit for adding the wires that go from the 2-wire plug on the alternator to the voltage regulator. This might be helpful:













*"Lastly (and this really determines where I go from here), I think I should upgrade to a higher output alternator, as I've had apparent power supply issues in the past and I do plan on installing a new audio system (and who knows, maybe other stuff like an electric fuel pump etc). But with as confused as I am already with the wiring, I'm lost as to what I should be looking for. I'd prefer to not have to change mounting brackets or do any custom work to install a new alternator, and I'd only like to do this once so I'm looking for one with a good output - maybe 120-140? Or is that just overkill?
And what's the deal with the "one-wire capable" alternators? I assume less wiring is better, but how does that translate to my current wiring situation? And internal vs external regulators? I assume internal is better...."
*
If you can make this decision now, you can accommodate your choice in the new harness.

A single wire alternator requires only the output wire from the alternator to the Solenoid "BAT" terminal. Simplest way to go.

Your alternator is externally regulated; it requires an external voltage regulator (the one on the firewall).

An internally regulated alternator will use a 12V feed from your harness (GM convention is a brown wire from the ignition harness) to provide the regulator with the required 12V "excitation" voltage. It would use the 2-wire white connector that you show in the picture.

Based on your comments and plans, I'd recommend a single-wire alternator that is rated for at least 95 Amps. At idle, you can usually expect about 75% to 70% of rated output, so you will have enough to run fuel injection and a fuel pump and a decent sound system.

If you're going to go with a different alternator, make the change now and incorporate the proper connections in your nes harness.

The AA kits are nice; they usually include clear instructions for wiring up any of the common alternator choices.

Good luck!


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## Chazz (Mar 8, 2010)

Thanks for the reply! Very helpful. So I guess the new AA harness was designed with an internally regulated alternator in mind. Another question: should I be looking for a 10si case or a 12si case on my new alternator? I assume my current one is a 10si, but would a 12si fit in its place? It seems as though the 12si has more options to choose from, but I found a Powermaster with a 10si case that might work....

http://www.summitracing.com/parts/pwm-57294/overview/make/pontiac/model/gto/year/1967

140 volts, not really that much more expensive than the lesser-voltage alternators. Thoughts?


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## BearGFR (Aug 25, 2008)

What you've got in the photos is the old style Delco 10DN - externally regulated (you already knew that). I don't know what else you're doing or have done to your car, but if you add addtional electrical load (electric cooling fans, big-honking sound system, HID lights, etc) it probably won't be able to keep up with the load. I ran into that problem on my 69. I wound up replacing the original alternator with a CS130 style internally regulated unit (spec'ed for a Pontiac Safari Wagon) that puts out 105 amps. The conversion wasn't hard, and the new unit fits just fine in the same space occupied by the old one.

Bear


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## jmt455 (Mar 26, 2012)

The only thing I don't like about that Summit Powermaster alternator is the black finish, but if that's what you want it is a good choice. 

We recently purchased a 100 amp, chrome plated Powermaster single wire for about $110 at a local swap meet (no tax or shipping), so if you keep shopping you might find a better price.


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