[64speed]

I upgraded my alternator from a external regulated alternator to a 3 wire internal regulated alternator because I had M&H build the harness to accept it. The wire that goes to the back of the alternator that mounts to the stud seems a little thin. Is it alright to hook it up to a higher output alternator? I ordered a 105 AMP alternator.

["QUICK-SILVER"]

What size is the alt. output wire? 10 AWG? 12 AWG?
What size is the fusible-link on that wire?
What size is the B+ wire feed from the horn relay/junction block?
What is the total amp load you plan on that single charge wire supporting with alt. at full output? That's all electrical accessories and keeping the battery fully charged.

At least one other thread you said you was going to ignore/disregard directions from the alt. manufacturer. They gave you those directions to keep you from burning up the fusible-link on the alt. output wire.

If you look at wiring diagrams for cars that came with high amp alts...You can see what kind of modifications you'll need to do to your car. Factory basically had the same thing the alt. company told you to do. On your car that would be an additional charge wire (with fusible-link) from back of alternator to battery + post or junction block on horn relay.

You can do this. And do it right the first time.
Clay

[64speed]

The alternator I have is 105 AMP. I called M&H today and they told me that 105 amp was on the very edge of what a stock wiring harness could handle. I am not running any additional accessories besides classic auto air and holley sniper fuel injection. I don’t think the alternator will really be strained or have to run at max capacity for these two items. I will have a radio but it’s the factory radio modified for Bluetooth with no amp or anything like that.

[Squidward]

When I rewired my Lemans with an aftermarket kit it included an extra heavier wire to run between alt output stud and the battery + terminal if running a high output alternator and heavy electrical loads. The theory is that a standard alternator/factory setup runs the charging wire back to the main power connection point, which may leave a fusible link in between the charging wire and the battery. If you have really heavy electrical loads connected downstream of the main fusible link, you could blow your fusible link by drawing too much current through the link. By the same token, if you are charging from a high amp alternator to a point where it has to charge a battery through the same fusible link, then it could also blow that link.

Another alternative is to run the extra charge wire from the alternator + stud to the starter + terminal. It hides things a little bit more.

When I ran the wiring for the CS130 in my Firebird, I ran an 8 or 10 gauge wire back to my battery from the alt stud. I was running an electric fan at the time, so I needed the juice.

FWIW, all of the factory loads, plus my FiTech, are within the capacity of a 63A 10si alternator. CS130's just have a better low rpm performance. But if you aren't running an electric cooling fan and high amp radio, then your system should be within limits. Your only problem will be if you discharge your battery significantly. Then you could have an overcurrent situation when your battery demands more amps to charge, and your alternator is capable of putting out more charge than your wiring can handle.

["QUICK-SILVER"]

Originally Posted by 64speed

I called M&H today and they told me that 105 amp was on the very edge of what a stock wiring harness could handle.

And that's with the cars "born with" electrical accessories

Originally Posted by 64speed

I am not running any additional accessories besides classic auto air and holley sniper fuel injection.

Your "not any" IS additional amp load. How much can you add to the "very edge" without going over?

Originally Posted by 64speed

I don’t think the alternator will really be strained or have to run at max capacity for these two items.

Of course it want be strained for those two items alone.

HEI, MSD, Sniper, AC...Just how many amps have you went past what the wiring harness can handle. That's the single charge wire.
Extra fuse box, using relays, isn't going to change the need for the extra charge wire.

Look at your wiring diagram and see if it don't show an optional charge wire for cars that had more accessories than your car came with.

Clay

[64speed]

I am going to use my HEI wire to power a supplemental painless wiring fuse box that has 4 keyed hot and three battery hot terminals powered by a relay. I will run my add on items off of it except for the items that have to be connected directly to the battery. So are you saying I can run a 8 gauge wire from the alternator post to the starter + side or to the battery and alleviate the power going thru the harness?

[Squidward]

Originally Posted by 64speed

I am going to use my HEI wire to power a supplemental painless wiring fuse box that has 4 keyed hot and three battery hot terminals powered by a relay. I will run my add on items off of it except for the items that have to be connected directly to the battery. So are you saying I can run a 8 gauge wire from the alternator post to the starter + side or to the battery and alleviate the power going thru the harness?

Yes. It would solve any question of battery charging capacity, because charging current would have the extra path of the heavier wire.

If you start to add heavy loads like electric fan, super thumpin' stereo amp, etc., then you should run those off the battery bus via a relay, etc.

Regarding the HEI wire and supplemental box: What loads are you going to run off that? You are going to run a Sniper with timing, so the FI unit should supply power to the ignition - no problem there. Just be careful to run the BIG stuff off the battery (with the extra charge wire from the alternator), and don't overload the regular fused system.

[64speed]

Originally Posted by Squidward

Yes. It would solve any question of battery charging capacity, because charging current would have the extra path of the heavier wire.

If you start to add heavy loads like electric fan, super thumpin' stereo amp, etc., then you should run those off the battery bus via a relay, etc.

Regarding the HEI wire and supplemental box: What loads are you going to run off that? You are going to run a Sniper with timing, so the FI unit should supply power to the ignition - no problem there. Just be careful to run the BIG stuff off the battery (with the extra charge wire from the alternator), and don't overload the regular fused system.

I really dread doing all this because I am not one of those people that has ever had luck running wires and making them look neat. I will run the sniper and the dual sync off the painless add a circuit strip. I will connect the parts that go to battery either at the horn relay on the inner fender or to the battery itself.

[Squidward]

Cool.

When I ran an electric fan I ran a 2 post electric breaker on my radiator support. I attached the charging wire from the battery + to a breaker terminal (we'll call it the supply side), and ran my electric fan feed off the other "load" side of the breaker. I also ran my heavier gauge charging wire from the alt + to the supply side of the breaker. Later, as I added loads like FiTech and MSD6AL, I added them on the load side post of the breaker. This breaker also became the tie-in point when I removed my horn relay, so the fusible link tie-in from the horn relay now got tied in at this same breaker with the charging wire.

Your fusible link is the last line of defense upstream of your fuseblock and fuses. It's pretty much just a 14 gauge wire, so anything that sends more amps to or from the battery greater than what a 14 gauge wire can carry, needs to be on the battery side. That's why a high capacity alternator needs a heavy charge wire that feeds into the electrical bus system at the battery, and isn't charging through a fuse, breaker, or fusible link.

Take the 1967 Firebird, for instance. The alternator output stud, the battery + post, the horn relay + terminal, and the starter + post are all the same point electrically: The battery. There is no breaker, fuse, or fusible link. So in re-engineering your small piece of the electrical, your wiring should already be setup with the alternator output post feeding the battery directly. Adding a new wire just increases the charge capacity. On the 67 FB, all of the fuseblock loads get fed via a fusible link attached to the horn relay + terminal. I would guess your 64 is similar.

So if you want to feed extra loads off your HEI wire, that's OK. But just be careful. At some point you could reach a constraint, whether it's a fuse, fusible link, or some wiring in between that can't cut the mustard. I don't think the ignition supply from the key is fused in any way except for the fusible link power. Is your add on strip fused so that you blow that fuse before melting your HEI feed or your ignition switch/wiring?

Sorry if I am confusing things. I realized that in my earlier post I implied the alternator charging wire might tie in on the load side of the fusible link. I confirmed that an alternator charging wire should not charge through a fusible link. Alternator charge wire goes directly to the battery.

[64speed]

Yes the painless add a circuit works off of relay and fuses. You just have to supply it a 12 volt keyed and a 12 volt constant source. My main concern is burning up my alternator wire with a 105 amp alternator

[Squidward]

Take an 8 gauge wire and run it from the alternator output post to the battery + or starter +. That will be all you need.

[64speed]

Originally Posted by Squidward

Take an 8 gauge wire and run it from the alternator output post to the battery + or starter +. That will be all you need.

Thank you for the simple and concise answer. I am bad to get caught up in the theory and the “but what about this”