After dealing with a mechanical fan on my 67 Coronet for a few years, I want to get a modern-internals alternator to give myself enough output at idle to run junkyard electric fans (and maybe get rid of my sealed beams to boot).
However, with how Mopar dashboards are wired (and apparently some other more recent cars like Samurais?), I can burn out the wiring through the in-dash ammeter if I just slap on a higher-output alternator since the ammeter itself is integral with the charging circuit.
The simplest piece of advice I could find for alternator upgrades on these cars was just running an 10 or 8 gauge wire between the alternator and either the positive battery post or the starter relay. More complicated upgrades include messing with the dash wiring... and having been under the dash on this thing a few times already I'd rather not.
Will just giving a better charge path to the battery solve the risks to the firewall/dash wiring? In an earlier bout of research I remember reading that the battery discharging/charging too fast was what could cook the ammeter, not the overall output. So, give a direct charge wire to the battery, safe wiring elsewhere? Or do I need to muck with the ammeter circuit directly too?
This is how my car is wired from the factory:
(above from here if it breaks: http://www.madelectrical.com/electricaltech/amp-gauges.shtml)
pres589
UltraDork
8/16/14 4:03 p.m.
If you bypass the ammeter like you're discussing with a cable between the positive battery post and the alternator, the ammeter won't function. There's no reason for electrons to want to pass through the ammeter's resistive shunt if they don't have to.
I think a re-wire with a modern fuse box, relays added where they make sense (like headlights) or are required (cooling fan add-on), and some kind of voltage display would be wise. Ammeters are nice but they aren't really needed if you can keep in mind what voltage levels really mean for the battery and have a decently accurate voltage gauge. For your path from alt to battery, I like that, and did it on my VFR a few months ago when I had a charge issue. It took voltage readings at the positive post of the battery from about 14.0 to 14.7VDC by going from the voltage regulator over a pair of 10 gauge wires to the positive post. I should really get around to fusing that run... Honda wired VFR's like mine like what is shown in your diagram and the starter solenoid is used as the path to the battery. There's a lot of voltage drop there on my bike; your Coronet may be better.
You could install a self resetting circuit breaker inline with the ammeter, like the ones typically used for power seats. It would effectively limit what could go to/through the dash. Then you could install an aux fuse box in the engine compartment for relay switched under hood loads like fans and lights.
As the past owner of a '67 Belvedere II hardtop, I demand photos of the '67 Coronet!
In reply to Secret_Chimp:
I'm working on this with my Barracuda now. I'll post something later in the day on Sunday after I get it sorted out.
put in a Delco CS alternator from any GM car or truck built from the late 80's until the early '00's- they made many styles, shapes, and physical sizes so finding one to fit should be easy.. run the powwer wire from the big stud on the back of the alternator directly to the battery.. bypass the ammeter altogether and put a similar looking volt meter in it's place.
In reply to Secret_Chimp: This is a temporary configuration for my car.
Today I ran a line from the output stud on the alternator to a power distribution block I mounted near the battery. It's not connected to the battery. The relays for the Spal dual fan unit are connected to the same power distribution block.
With the car running, kicking on the fans does not cause the amp meter to peg to full charge. By not connecting the high amp load in line with the battery the load isn't running through the gauge. The amp meter just sees a slight discharge in the system. I have a VDO volt meter mounted in the glove box. The fans running dropped the system down to 12 volts from 14. Kicking on the lights dropped it below 12. The load is too much for the Powermaster version of the Chrysler squareback alternator. A stock 36 amp alternator wouldn't have a chance with just one fan.
I'm running the March bracket and pulley setup in my Barracuda. I just tried mocking up a couple different alternators on the March bracket. No luck. I'm going to need to either fabricate a new bracket for a Denso or Bosch alternator, or pony up for one of the Flaming River billet ones. 
I'm thinking about bringing in a mini Denso 100211-6051 and mocking it up. It's a 120A unit for a Deere tractor. Looks to be the same (or similar) case to the mini Denso popular with racers.
What engine is in your Coronet? Depending on the brackets, you might have a better time bolting up a late '80's Mopar/Bosch alternator.
It's the original 318, iron water pump/timing cover.
