Constant heavy charging
Thanks Mattax for you response and I think I understand what your saying, just not clear on the modification you are suggesting. Holley wants it connected directly to the battery but didn't allow for this issue. Is there reason for concern that the fusible link might go out?
I think Holley & Autotronics (MSD) people had either one of two reasons for saying that.
1. These are relatively big draw items so they wanted a dedicated wire, and they
assumed the battery and the alternator are closely connected in most cases.
2. Something inside their product is relatively sensitive to electrical noise or voltage ripple and the battery might act to dampen that.
3. A variation on the above two is the opposite concern. That these items won't turn on during start up because of the low voltage while starter is cranking. So they suggest the most direct connection to the battery.
OK. That's three possible reasons...
My guess is the first one is closest to the mark. Instructions are a generalization and don't account for systems like ours.
Concern about the fusible link. Yes a little. Even though its a short length, its only 16 gage wire.
Concern about the bulkhead connections. Yes. Depending on the year and options, it may be just one Packard 58 connector on the alternator feed, and same on the battery charge/feed.
Lets say the average current to the Fitech etc is 15 or 20 amps. Then that's 15 or 20 amps constantly though all of those connections and wires in addition to what they normally carry.
There could be enough resistance in the fusible link that it will get warm passing 20 amps for long periods of time.
Also, after start up, the link and attached wiring also will carry the current for recharging the battery. Add another 15 to 20 amps for a total of 40 amps. Even though the high charging rate may be less than a minute, IMO 40 amps is not something the circuit should see on a regular basis.
The alternator output connection through the bulkhead will also carry current for everything else that might be on.
Alternator field circuit - 0 to 3 amps
Brake lights
Heater fan
windshield wipers
etc.
This is why the alternator output side is probably the most vulnerable to overloading.
From around '66 to around '74 the alternator output through the firewall is a single wire with a packard 58 type terminal. That's probably the weakest point in the system.
The fact its all working for you right now is great.
These are things to look out for and I think you want to plan for addressing.