To the C body braintrust: What year did Mopar upgrade to the square back type alternator?
This is an old thread, but I'll add some to it... In sum, the "square back" alternator was introduced as standard on all 1972 models.
From the 1972 Service Highlights:
Some additional, broader, general information from a post I wrote for Moparts:
The Chrysler designed aluminum housing alternator was introduced in 1960 on the Valiant and Lancer models. This alternator had the informally termed "round back" style rear end shield. Chrysler called the two housing, or case, components "end shields". These alternators have one grounded brush and one field connection. This style continued through 1969 with a slight change in the spacing between the fins when comparing earlier Essex built versions and later Chrysler built versions. These alternators were used with an electro-mechanical voltage regulator. This regulator functions by switching +12V DC on and off to the alternator field lead to regulate system voltage.
In 1969, a special alternator was used with the new transistorized regulator in some models. This is the "Insulated Brush" alternator that looks much like the regular alternators of 1969. The difference is the grounded brush of the prior and other 1969 alternators is insulated from the rectifier, or back, end shield. The 1969 only transistor regulator looks like the 1970 and later regulators with the addition of a third terminal lead called the suppression lead, in addition to the ignition and field terminal leads. Other 1969 models not so equipped still used the grounded brush alternator and electro-mechanical voltage regulator.
In 1970 models, the alternator and voltage regulator were again redesigned. The new "Isolated Field" alternator still used the "round back" style end shield although it is slightly different without the grounded brush. Two isolated field connections were now used. This "round back" style was used through 1971. The voltage regulator now contained only two terminal leads, ignition and field. This is why the triangle shaped connector looks like it is missing a lead, because it is. The connector and regulator case are carryovers from the 1969 transistorized regulator with different internal electronics. The regulator functions by switching ground on and off to one alternator isolated field lead with the other field lead connected to +12V DC (Ignition Run). The regulator action is adjusted for temperature too. This regulator was used through the 80s on cars (with a change in 1975 for the different 100 Amp alternator, a slight revision in 1980, and some other slight application variations), and early 90s in trucks.
For the 1972 models, the rear end shield was redesigned in the informally termed "square back" style. The end shield contained a different mounting for the rectifiers and capacitor and connected to the stator without soldering. This simplified assembly and service operations. The electrical functioning of the alternator and voltage regulator remained the same. This particular "square back" style was used through 1977.
For the 1978 models, the end shields and stator were redesigned again. The most visible difference is the "thin" edge of the stator between the two end shields. This is still the "square back" style, but is available in higher capacities than earlier models. This alternator style was used from 1978 through 1987. These alternators can interchange with the earlier versions, but some alignment adjustment might be needed.
Chrysler also used other alternators not included in the foregoing into the 90s such as Leece-Neville in the 60s and early 70s, the Chrysler 1975-1987 100 Amp and 114 Amp, the 90 Amp and 120 Amp Chrysler units introduced in 1988, and Nippondenso.