Motorola, as used by AMC

Overview:
AMC used Motorola alternators 1965 through 1975. You can tell the differences between the styles and years by their use of "isolation diodes" in an aluminum heat sink that was normally painted red.
The 1965 through 1970 35 amp unit had a single isolation diode, the 55 amp had twin isolation diodes on one heat-sink.
In the years 71 through 75 AMC Motorola used an internal diode trio more like the GM and they came in 37, 51 and 62 ampere rated models. The stator winding of the 37 amp model was wye wound where the others were delta wound.
Alternators use in conjunction with 4bbl carburetors in the early 70's may have an additional connection to supply the choke heater with 7vac. This terminal would be located in the negative diode assembly.
An alternator date code was typically stamped at the back of the rear housing in large black ink numbers. For example 185418 = 185 would mean Motorola (MFGR) then 4 would indicate year (3 for 1973, 4 for 1974, etc) and 18 (week of the year)
Starting with 1976, AMC dropped the Motorola system.

Wiring a Motorola or AMC alternator:

From regulator to alternator:
Black to ground on alternator - typically a spade terminal next to the field connection.
Green to field. This is direct from regulator to alternator, no other connections or feeds and is a spade terminal connection at the alternator - where the brushes are.
Orange to "stator" or "aux" on alternator (called the regulator terminal).
Regulator to other:
Orange with tracer goes to the alternator indicator bulb in the dash.
Yellow wire to coil primary feed (and thus to IGN terminal on starter solenoid)
Alternator connections:
Large red wire goes to bat or battery terminal which is the large post next to the isolation diode on the heat sink - the red aluminum part.
Since the regulator does not ground through its case, but through the alternator, it's a good idea to make sure the alternator is firmly installed and grounded to the engine - normally the brackets will do a good job. Further, the engine itself must be well grounded to the chassis. Typically this was covered by a heavy ground strap or cable from the engine block to the cross-member, near or at the motor mount on the right side.

The 1965 Motorola regulators used only 3 wires - Black, Green and Orange.
In 1966 an additional wire was added - the yellow ignition feed or "exciter". This "excites" the system. It comes from the coil feed on the starter solenoid. Otherwise the alternators were the same 1965 through 70.
In 1971 the isolation diode was replaced by an internal diode trio.
The orange stator (aux or regulator connection) wire goes to the regulator orange and to the dash light (orange with tracer). When you turn on the key, 12+ is supplied to the dash bulb, through the regulator and is directed through the brushes through the field windings to ground. This causes the light to be "on" when the key is on but the alternator not running or charging. If the bulb does not light when you turn the key on, you may have a defective bulb, a bad regulator or worn brushes in the alternator.
When the alternator is working, the output voltage at the aux or stator terminal is the same as the voltage supplied to the bulb through the key switch so no current flows - voltage is approximately the same on each side of the bulb so it won't "glow".

If everything is correct, the bulb won't glow!
I hear a lot about the so-called "Rambler glow" that is supposedly normal with Rambler/AMC vehicles using the Motorola charging system. On a properly working system that is up to spec with no abnormal voltage drop across connections, this is NOT normal.
Because the indicator bulb is in parallel with the isolation diode(s) there is roughly a .7 volt drop across the isolation diode (due to internal resistance of the diode). This is not enough to cause the light to glow, but with an incorrect bulb installed, or an abnormally heavy load on the alternator, or a faulty isolation diode, the light could glow, more visibly at night. I have used a 1v source across a charging system indicator dash bulb to attempt to observe such a "glow". In fact, 1 volt made the filament barely glow enough to see when it was not in the dash or covered with the green filter plastic - showing that 1volt should not cause a glow when it was installed and observed through the green filter plastic of the dash.
If the bulb glows you may have an isolation diode going bad or poor connections. In the case of a glow with a 1971 through 1975 model Motorola, it is likely a diode trio that is out of spec.
Please note - the isolation diode or diode trio could still check ok using the old "go/no go" tests but be failing or have developed enough internal resistance to cause the indicator bulb to glow. In this case, replace the isolation diode or diode trio. This will typically solve the "glow".

To check alternator functionality, you can trick the alternator into putting out it's full output by "full-fielding" it. To see if the alternator will charge, with the engine not running and the key off, disconnect the green wire from the alternator and instead connect a jumper wire to the field terminal on the back of the alternator. Start the engine and connect that jumper to battery voltage. NEVER connect battery voltage to the green regulator wire! The altenator should put out full output - at least 14 to 16 volts.

If you need a new or replacement regulator, make sure to get the correct one to match the correct year/type of alternator as the setting were a bit different for the ones with isolation diodes vs. the diode trio. Also note that 71-75 alternators may have a connection used for 7vac electric choke. Do not use this for choke stats requiring 12v and do not connect regulator wires to this connection!

Below is a basic schematic of the connections to an early Motorola system as used by AMC

Click thumbnails for a larger view:

Above, a basic wiring diagram for 1970 AMC Motorola charging system. This is fairly representative of most AMC systems of that era.	Above is a view of the rear of a 55 amp Motorola alternator. Note the two isolation diodes, one on each side of the BAT terminal.
A 35 amp Motorola alternator with the terminals labeled.	A 35 amp AM alternator. Note the isolation diode is internal, otherwise all connections are the same or similar.
Above is a typical Motorola alternator used after 1970 - 71 through 1975, showing connections used. (click for larger view)

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