Diagram #1 shows the basics of the early alternator / voltage regulator (VR) design. There are 2 brushes in the alternator, each one has a field terminal, one is labeled "FLD", the other is labeled "GND". The GND brush is grounded with the brush mounting screw. the other brush is the (+) brush (or field) and attached to it is a green wire that routes over to the voltage regulator (which is behind or near the brake master cylinder) this green wire is connected at the voltage regulator at the "FLD" connection. The other connection on the regulator is a blue wire with a female plug end. This is the "IGN" Ignition side.
Basically, the voltage regulator completes the charging circuit and allows the alternator to charge the system. When a certain preset voltage is obtained, the regulator "opens" (or turns off) the circuit until the electrical system's voltage drops below a certain point, then it turns on again. The old Voltage Regulators are repairable and rebuildable. The 1969 Dodge Shop manual (available from Year One) details how to do this. If you think your regulator is failing, open it up and clean the "points" with some emory paper or light sandpaper. Sometimes these points get corroded and this stops them from working.
NOTE: in dia. #1, the FLD is generally green, and the IGN wire is Dark blue on stock Chrysler wiring harnesses.
There are a number of reasons one might want to upgrade a pre-1970 charging system to a newer solid state (transistor) voltage regulator. The list of reasons include:
Below is a diagram showing how to install a 70's Voltage Regulator on a sixties mopar:
Basically, a wire is added to the second Field brush on the alternator. On the orignal
alternator, this brush is grounded to the case of the alternator, so you'll need to either
change the alternator to a 1970 or new style, or adapt the newer brush set to the old
alternator. The brush set costs about $5 at your local parts store. The second field wire
is connected to the outside plug on the newer voltage regulator. (two plugs, one is in the
middle, one is on the outside). The original field wire that ran to the "FLD"
plug on the original regulator (green wire) needs to be connected with the wire that ran
to the "IGN" side of the original regulator. This wire (both the old FLD and the
old IGN) need to be connected to the center plug on the newer regulator as well. One other
important thing is, the new regulator must have a good ground (-) signal to
its case. Mount the new VR to a fender or the firewall and be sure to sand a
little paint off the fender and the case so you have a good ground. If there isn't a good
ground to the new regultor case, the charging system will not work properly!
Another wirning diagram.