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  Mopar Alternator Overview
Mopar Alternator Overview 1960-1970+
Alternator History

Chrysler first introduced the alternator in the 1960 model year.  Due to the increased electrical loads on the charging system the old generator could no longer provide enough amperage (electrical volume) to operate all of the electrical components on the car.  An alternator is a three phase AC (alternating current) generator which uses three positive and three negative diodes to convert the AC voltage to usable DC (direct current) voltage.  All six diodes are a can type that was pressed into an aluminum frame.  Diodes produce a fair amount of heat as current is passed through them and the aluminum frame made for an excellent heat sink to dissipate this heat.  Heat and vibration is the worst enemy of any electrical component.  The three negative diodes, identified by their black lettering, are pressed directly into the alternator rear frame.  The three positive diodes, with red lettering are pressed into a separate frame which is attached to the rear frame with the output battery stud and a thin mica insulator keeping the two separate electrically.

The first alternators used on Chrysler products was made by a company called Essex.  The Essex brand Chrysler alternator can be identified by the wide spacing of the fins on the front and rear frames and will also have the Essex symbol cast into both of the frames.  For the 1963 model year Essex continued to make the alternators for Chrysler, however they added more fins to the frames to give it added strength.  Essex also produced the first mechanical voltage regulators for Chrysler and had the Essex symbol stamped into the metal case of the voltage regulator too.  These were all single field, "B" circuit alternators.  By 1964 Chrysler was ready to manufacture their own alternators which looked like the Essex brand but no longer carried the Essex symbol that was cast into the frames.  These were produced in 37, 46, and 60 amp versions and all looked the same on the outside.  Chrysler still retained the same "B" circuit, single field wiring design through the 1969 model year.  In 1970 electronics were starting to come into their own and we started to see the electronic voltage regulator.  When Chrysler went to the electronic voltage regulator the wiring design changed from the single field "B" circuit to the double field "A" circuit, which now had two field terminals on the back of the alternator.  The frame design stayed the same and another terminal was added for the second field.  This style alternator stayed in production through the 1971 model year.  For 1972 Chrysler redesigned the alternator.  The front frame stayed the same, but the rear frame changed considerably.  Instead of the can type pressed-in diodes used in the earlier alternators, they now had a positive rectifier and a negative rectifier each containing the three diodes.  These were bolted to the rear frame as two separate assemblies which made a common electrical connection that the stator windings also connected to.  This style of alternator greatly improved the repair aspect as no soldering was needed to join all of the diodes and stator windings.

Alternator Date Code Markings

Now on to the markings of the Chrysler alternator.  As you know Chrysler went to great pains to mark and identify almost every part that went into the creation of all their cars.  The alternator was no exception.  Both the front and rear frame had a "pie" casting date cast into the frame when it was made.  This was divided into twelve sections each representing a month of the year with the year cast into the center of the pie.  Each section of the pie had raised dots identifying the week of the month that the frame was cast.  Three dots in the third section of a pie with a "69" in the center would mean the frame was cast in the third week of March 1969.  The front and rear frames on any particular alternator may or may not have identical casting dates.  They could vary by several weeks or even months.  At the time the alternator was then assembled, the date code was stamped on the pad above the battery terminal just below the part number which was also stamped into the rear frame.  This was a three or four digit code with a space between the first or second digit and the third digit.  The first and/or second number was the week and the last two digits was the year that the alternator was assembled.  A date of "1 68" would mean the alternator was assembled the first week of January in 1968.  A date of "42 68" would be the second week of October 1968 and would be used on a 1969 model year car, since the new model years began in the fall of the previous year.

On a correctly coded alternator the assembly date must be later than the casting dates of both the front and rear frames and earlier than the build date of you car.  The bottom of the diodes also had identifying numbers printed on them.  Most of the diodes were manufactured by Motorola for Chrysler.  Some had the Motorola symbol, which was the letter "M" inside of a circle, printed in the center of the diode.  Around the outer edge of the diode was the Chrysler part number and the manufactured date of the diode.  The date code on the diode was also a four digit date of which the first two numbers designated the week of the year and the last two the year, similar to the assembly date of the alternator except that there was no space between the numbers.  These dates must also be earlier than the assembly date stamped on the alternator, but not always earlier than the casting dates on the frames.  Chrysler also attached a red warning tag to one of the field terminal spade connectors on the back of the alternator.  It read "WARNING DISCONNECT REGULATOR BEFORE TROUBLESHOOTING".  This was put on the alternator because when repairing the charging system even an intermittent grounding of the field wire would burn out the voltage regulator.
 

 

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