The first internally regulated alternators (16ACR 69-71) used two plugs to
connect to four terminals - the main charging terminal, a battery voltage
sensing terminal used to control the regulator - both brown that went to the
battery cable on the solenoid, and two terminals that the ignition warning
light - brown/yellow, was connected to. This last went to one terminal in
each plug and I suspect was a way of protecting the alternator should one of
the plugs fall out.
On the face of it both brown wires would be at the same voltage as they went
to the same place, so in theory voltage regulation could be done by a simple
internal connection inside the alternator. But under high current
conditions there will always be a volt-drop in the main charging wire from
the alternator to the solenoid, which will result in a lower voltage at the
solenoid than is being output by the alternator. Battery sensing uses the
voltage at the solenoid to control the regulator, which ensures that the
required voltage exists at the solenoid at least, even though that resulted
in a higher voltage at the alternator output terminal.
The next alternators (also 16ACR 1972) used a three-pin plug with one large
spade for the charging wire which went to the solenoid, a standard-sized
terminal for the brown/yellow indicator wire, and a third terminal of a
different shape or size for the battery sensing wire which also went to the
solenoid.
Subsequently this alternator was modified to have the regulator sensing wire
connected internally to the output wire, and these are machine sensing
instead of battery sensing. The same 3-pin plug was used, I don't know what
the third terminal was like.
The next variant was the 17ACR (73-76) which used the same three pin plug
but seems to have reverted to battery sensing again, possibly because of low
voltage at the solenoid.
The final variant was the 18ACR which reverted yet again to machine sensing,
using the same 3-pin plug but now had two large output terminals plus the
indicator terminal, and two thick brown output cables from the alternator to
the solenoid, and up to a splitter by the firewall. Two output cables
halved the volt-drop under high current conditions.
73-76 i.e. battery sensing wiring is directly compatible with the later
machine sensing alternators with the two large output terminals, the thinner
brown wire just acts as an additional output wire, which reduces volt-drop a
little.
The same can be said of the earlier four-pin, two plug alternators if at
least the thick brown and the correct brown/yellow are connected to the
plug. The thinner brown can be connected to the spare output terminal for
additional current carrying capacity, if not it must be carefully insulated
and not allowed to come into contact with anything, unless it is detached
from the solenoid and securely taped back. The brown/yellow that comes from
the warning light should be identified and the remaining two taped back out
of the way. If the two brown/yellows are left connected together then that
should be safely insulated and the single brown/yellow used for the plug, or
vive-versa.
PaulH.
----- Original Message -----
>A little more on this. I see 3 brown/yellow wires:
> 1. Connecting to the small pin (of the group of 3) on the alternator.
> 2. Attached to the old 3-pin connector (which is hanging loose, so not
> connected to anything)
> 3. Hanging loose.
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