|It is critical to understand how the charging
circuit is wired into the rest of the electrical
system. Even if you don't work on the car, you can
prevent a fire by understanding that the charging circuit
can not handle high loads for any length of time. If
the ammeter swings far to one side or the other and does not
quickly return close to center, the circuit will fail.
The fusible link should fail first, but any loose or
oxidized connections may melt and even ignite nearby
flammibles before that happens. The ammeter shows the
amount of current flow to or from the battery.
How and why this circuit can not support sustained high loads, and what can be done solve various problems is covered below.
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
The battery is recharged by the alternator through
a wire that also connects to the wiring main junction.
Notice the main junction is located between the alternator and the ammeter.
Internally the ammeter has a shunt that carries most of the current.
When the battery is fully charged, no power flows
through the charging wires or ammeter.
Current from alternator goes to main junction.
Only current for recharging the battery goes through the ammeter.
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.
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.
3. Another option is to rewire the circuit using a remote shunt and ammeter, or voltmeter instead of the integrated 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)
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.