Alternator amp rating.

[James Camp]

thanks,i forgot about seeing all the factory splices on the black wire going to ammeter when i unwrapped the wiring harness under the dash, but i remember tracing the wires to light switch,ignition,and fusebox,, i didnt add anything extra inside the passenger compartment, its all stock, but what bothered me, i put an aftermarket a/c blower and evaporator under dash but had wired it thru a grommet and by passed the bulk head with the compressor, and evaporator blower,i put a new a/c compressor with the bracket off a Ramcharger, and the original alternator off the 74 duster didn't match the 90 model bracket, so when i replaced the alternator to a 90 model alternator , 80 amp was the smallest amp alternator i could find, after getting everything bolted together with nothing on , no lights,radio or a/c, the alternator pegged at 40+ when i started it,,,didn't want to have a meltdown, so i shut it off,it may have been that the alternator would have dropped back to normal when the battery was fully charged, i put an ohm meter on the battery before starting it, was 12.7 volts,after starting it .ohm meter showed 13.7, looked at dash and i saw the alternator was all the way to top at 40+,thats when i shut it down,the battery may have need charged,because i had moved the car inside and out of the garage with temporary wiring to the ecu and no alternator hooked up,,,I got a 74 that had the seatbelt interlock module, so i had pulled wiring harness out of 73 duster and replaced all underdash wiring and underhood, wiring under dash i unwrapped and checked bulkhead and all wiring, retaped it and put it in flexable plastic conduit, and had unwrapped all underhood wiring, and put eyelets on field wires alternator and resoldered factory splice on blue wire, retaped wiring and put in conduit, have replaced voltage =vr, starter and ecu and starter relay, wanted everything new i could replace, plan on giving car to my son in future,

 

[Mattax]

i put an aftermarket a/c blower and evaporator under dash but had wired it thru a grommet and by passed the bulk head with the compressor, and evaporator blower,

Ah ha! This may relate to the issue. It shouldn't because none of the equipment was turned on, but it all depends on how the new wires were run, and where they connect.

i put an ohm meter on the battery before starting it, was 12.7 volts,after starting it ...showed 13.7,

Using voltage of the battery provides only a rough indicator of the charge state. 12.7 Volts is ballpark OK.
A better test of charge state using voltage measurement alone is what it drops to when the headlights are turned on, or as some factory manuals suggest, during starting.
Considering the situation, definately recharge the battery. First because we know it was run down a bit as you describe. Second, to see if that alone resolves the high current draw indicated by the ammeter.

the alternator pegged at 40+ when i started it,...
13.7, looked at dash and i saw the alternator was all the way to top at 40+,

The ammeter should only indicates current to or from the battery.
The ammeter should not indicate alternator output.
Take a look at the main power and charge circuit diagram below.
Power distribution occurs at the main junction. Notice the ammeter is in the wire going to the battery, which after the main junction.

When the alternator is producing enough power, its output voltage is higher than the battery's - around 14.3 Volts, give or take 0.5 Volts. All power needs are then supplied by the alternator. At the main junction it divides to the various systems where there is demand. The ammeter only shows the current flow going to recharge the battery.
While an ammeter could be placed on the alternator output before the main junction, that's not what the factory ammeters were set up to do. The factory ammeters can not handle that much current on a close to 100% duty cycle.

There is a chance that something was changed in the rewiring which has resulted in high current going through the ammeter even at idle.
In other words, we may be looking at a power draw for something in addition to simply battery recharging. Ignition alone should draw only a few amps, and same with the field circuit.
When the car is being started, the battery supplies power to ignition and starter relay, so the ammeter should show about 5+ amps discharge.
After starting, the ammeter should show battery Charging (+) and after a few minutes show no flow.

 

[Mattax]

Power Flow after start showing low rpm recharging.
(12.8 Volts across the cells is slightly misleading. It's what the battery voltage would be if the engine was shut off and the battery allowed to sit a few minutes. As long as the engine is running, the voltage at the battery positive will be the alternator output voltage, or close to it.)

 

[67Dart273]

A simpler way to look at this might be to simply state that "normally" in an ammeter equipped vehicle, all loads except for the starter are taken off the ALTERNATOR SIDE of the ammeter. What this causes is the following:

With the engine off, or the alternator not charging, the battery is now more positive than the alternator output. Loads such as headlights causes a flow such as to deflect the ammeter negatively.

When the alternator is outputting MORE positive than the battery, the alternator now becomes the supply source. This shows a positive deflection as the battery is charged

When the battery is exactly fully charged, and the alternator is properly putting out the nominal 14V, any loads such as headlights will cause the VR to ramp up and correct the added load back to 14V. So as you turn on the headlights EG, the needle might flicker a bit for a second, and then return to center. This is because the battery is balanced, there is no flow through the meter. The headlights or other loads are getting their power source from the alternator.

Incidently in your diagram power flow is backwards. The actual electron flow is neg to pos. I often describe this as the "functional circuit path" meaning many people think in terms that "power is supplied from" Most/ nobody thinks in terms of "it is supplied from ground LOl

 

[Mattax]

The actual electron flow is neg to pos. I often describe this as the "functional circuit path" meaning many people think in terms that "power is supplied from" Most/ nobody thinks in terms of "it is supplied from ground LOl

Yes, true about the electrons! Just easier for people to think of power flowing from high voltage than how the electrons actually move. LOL is right!
Maybe a bigger sin in that second diagram was not showing the grounds. After all, no circuit completes if it doesn't connect back!