|· The ammeter shows the amount of current
flow to, or from, the battery.
Recognizing when the ammeter is showing normal as opposed to problem conditions is critical. If the ammeter stays far to either side there is a problem. High current can overheat wires and connections. The result can be melted wires or even a fire.
Only in extreme situations should the fusible link, if present, fail first.
· Many 1960s and 70s Chrysler ammeters were labled 'alternator' on the gage face which can be a little confusing. Think of it this way: If the battery is discharging under normal driving conditions, something is wrong in the alternator circuit.
Wire Diagram; Alternator to Battery
Charge System Operations
- Run when battery is charged
- Run when battery is slightly discharged
Complete Charging System Wiring Diagrams
page 2: How Fusible Links Work in Charging Systems with Ammeter
Ammeter needle moves in response to
electrical flow. In the most common automotive ammeters,
the needle is deflected by the small magnetic forces created
when current flows through the meter. These meters are
placed directly in the flow path being measured. Some cars
received externally shunted ammeters. They indicate the same
information, but are wired in differently.
Automotive ammeters are wired to show the battery is discharging, charging, or neither.
Cars and trucks have two power sources, the battery and the
alternator. The output wires for the battery and
alternator is joined to the wires feeding the key switch, the
headlights, and fuse box at a one or more junctions. On
vehicles with an inline ammeter, this junction is usually a
welded splice under the dash.
When a car battery supplies power, by common convention we say
electricity flows out from the positive post at 12 volts.
The current eventually flow to ground and up the battery
negative cable. When a battery is getting charged,
electricity flows into the positive post.
Electricity always flows from the highest voltage power
source. For a battery to be recharged, it must be supplied
power at a higher voltage. An alternator generates power
at 13.9 to14.9 Volts. Therefore it is capable of
recharging a '12 volt' battery
While the alternator-battery circuit is often called the charge
circuit, its more than that. It supplies power for everything
but the starter. Power will come from either the battery
or the alternator.
Notice the main junction is located between the
alternator and the ammeter.
When the engine is running, no current from the alternator flows through the ammeter except to recharge the battery.
The output wire from the battery also serves as its charging wire. All ofthe wires connected to the battery are always hot!
To protect against an accidental grounding of the battery a fusible link was placed in the output wire (after 1964).
The battery may supply over a 100 amps for several seconds
directly to the starter when the relay closes.
A relatively small amount of current trips the relay and powers the ignition.
Current from alternator goes to main junction.
Only current for recharging the battery goes through the ammeter.
When the battery is fully charged, no power flows
through the charging wires or ammeter.
1. Check for oxidation, corrosion, loose connections especially at bulkhead. Clean, tighten, fix as needed.
2. An option is to create better connection or directly wire the feeds through the firewall, either in parallel to, or replacing the bulkhead connections.
This is essentially the same as Chrysler's modification for certain fleet use applications and keeps the ammeter.
Another version of this concept was used for later A-bodies equiped with rear window defroster grids.
3. In theory an option is to rewire the circuit using a remote shunt ammeter. At least some Chrysler vehicles used a remote shunt ammeter starting in 1976 as did some other companies (but not AMC/Jeep). (ref. Rick E. Mopar Action reprinted at allpar.com) Aircraft supply houses are another source of remote shunted ammeters/
High Rate of Charging: Maintain battery in good condition. If battery is low, keep alternator speeds down and monitor ammeter. Shut off if current is excessive. Use an alternator that can keep up with expected power needs at idle. Do not simply use an alternator that is rated high output, especially if not needed. Output goes up with rpm, if the extra current is not needed but the battery is low, it will send all that current into the charging circuit.
* Photo sequence of low battery being charged. (posted on For A-Bodies Only).
* More info on alternator rating games, on Speedtalk forum
Circuits: If adding headlight relays or other high current circuits, draw power directly from the alternator. Add fuse or circuit breaker for each new circuit.
Complete thread by NachoRT74 et al on improving the charging system while keeping the ammeter. (on Dodge Charger forum)
1986 AMC Full Size Jeep (SJ) Charge and Headlight Diagrams
(has their own pages)
1967 Plymouth Barracuda:
Typical of alternator systems using positive field regulation (single field wire at alternator).
Wire colors will vary with year, make, model.