Marko's sinister black ragtop...
Marko's sinister black ragtop is all business with a stout solid-cammed 7,000-rpm 340 coupled to an 833 four-speed. The stock charging system was no match for the electrical demands of the big fuel system, the electric fan, and the ignition, especially at night. The wipers weren't a problem, though.
Do you own a '69-or-earlier Mopar musclecar? Unless it has already been upgraded, the charging system consists of the old "weak sister" single-field alternator and its accompanying mechanical points-style voltage regulator. Ever wonder why those lights dim when the engine's at idle? With only 35 amps max output in standard V8 form (and 26 amps for sixes), by today's standards these old alternators are pretty feeble. Moreover, at idle the situation is much worse, with the alternator putting out only a fraction of its rated capacity at low rpm.
Due to the slow on/off nature of these old mechanical regulators, the swing from discharge to charge is too wide for many modern electrical components, including Mopar's electronic ignition. The electronic ignition may work, but with the voltage swings inherent in the points regulator, the factory didn't recommend the old-style regulator with the new ignition system. In fact, when electronic ignition made its debut as a production system, Chrysler had already switched to solid-state electronics in the charging system with the electronic voltage regulator and the corresponding dual-field alternator. For racers who wanted to retrofit to the new ignition system, a race-only, constant-voltage regulator was offered through Direct Connection (now Mopar Performance) to make their ignition system compatible with the old charging system. Though you were able to run the constant-voltage regulator on the street, the factory always maintained this regulator wasn't made for continuous duty.
These days, handling the electrical load with power-hungry aftermarket components, such as high-powered ignitions, fuel pumps, electric fans, and the like, will tax the stock charging system well beyond its output, so you may find yourself asking for jumper cables at the next cruise night. Even worse, some ignition systems will simply shut down if the battery's voltage drops too low; not a good look.
OE Mopar alternators were continuously upgraded throughout the years, both in max-rated capacity and low-speed charging ability. In 1985 the Chrysler alternator was redesigned to produce 78 amps, which was higher than the previous alternators. Starting in 1985 this alternator was used in M-Body Mopars and, with the exception of the narrow center band, was similar in appearance to the older alternators. Though the mounting points and wiring were identical to earlier alternators, the slightly wider body limits the belt adjustment to the outer two thirds of the stock range in most applications. Upgrading to a later version of the Chrysler alternator is a no-brainer mod for '70-and-later cars already equipped with a dual-field alternator. If you have a '69-or-earlier Mopar equipped with a single-field alternator, switching requires some minor changes to the wiring and a swap to the late-model regulator.
What's involved? Certainly, a lot of us would rather tear down the motor and swap cams than deal with the electrical system, but switching from the early-to late-charging system is quite simple. The original mechanical regulator had two wires going to it: a blue ignition-on wire feeding it juice and a green wire going from the regulator to the single-field plug-in at the alternator. Guess what? The solid-state electronic regulator also has a two-wire hookup: a blue ignition-on wire and a green wire going to an alternator field; same-same.
The stock single-field alternator...
The stock single-field alternator was already a sissy unit and was made worse with the underdrive pulley. Can you say "discharge"? The trunk-mounted battery managed to.
Our Chrysler 78-amp replacement...
Our Chrysler 78-amp replacement alternator (left), like all '70-and-up Mopar units, requires two field wires (arrows): one is the original green wire from the regulator and the other is an ignition-on hot wire, which we'll add. To the right is the stock single-field piece. Note the different rectifier style with the new alternator's square-back style, used from '73-and-up in alternators of various outputs. The old alternator is the earlier round-back design, which came in both single- and dual-field versions.
Up front, the new alternator...
Up front, the new alternator has a smaller pulley than these on the aftermarket piece on the old alternator. The small pulley increases the alternator's rpm, significantly adding to the idle output. Our replacement alternator came with a dual-pulley arrangement, but don't worry; the rear groove lines up in the same location as the stock single pulley. For looks, the pulley could be changed to a single-groove piece, but we didn't have one in a stock diameter. To swap pulleys, a special puller is required to properly remove the old one, and the alternator needs to be partially disassembled by removing the rear case to press on the replacement without damaging the alternator. The new, late-model, high-output alternator has the narrow band between the two aluminum casting halves.
Here's the regulator we found...
Here's the regulator we found on Marko's car. It's an aftermarket replacement for the stock single-field mechanical regulator. Some of these aftermarket replacements are better than the stock mechanical item and are actually electronically switched, thereby improving the charging system. Their effectiveness varies from brand to brand; buy quality parts here. Two wires are the stock hookup: a blue ignition-on wire with a spade terminal and a screw-retained green wire, which goes to the stock alternator's single-field terminal.
The new-style, solid-state regulator requires a special connector to hook it up. A connector can be hacked with a few inches of spare wire from the boneyard and can even occasionally be found in the electrical section of the local parts emporium. Swapping requires clipping the original terminals off the two old regulator wires and splicing them to the connector to plug into the new-style regulator. The only missing link is the second field wire on the alternator, but it's a piece of cake; the second field wire is merely an ignition-on jumper wire coming off the same circuit as the blue wire already going to the regulator. Just splice into the blue wire at the joint to the new regulator plug and run it to the second field terminal on the alternator. Now the two field wires will be connected to the two-field terminal at the alternator, but which is which? Actually, it doesn't matter which field wire is connected to either of its spade-type field terminals.
When upgrading to a higher-capacity charging system, make sure the wiring is up for the job. The factory setup fires all the alternator's juice through the bulkhead disconnect, through the ammeter, then back to the battery via the connection at the starter relay. The bulkhead-disconnect connections and the stock ammeter are the weak links here; both could burn if the connections are poor, thereby increasing resistance. With the 78-amp Chrysler alternator and sound connections, we've used the stock wiring without failure. An operable fusable link, available at most parts stores, is good insurance. If trouble or overheating wires are evident, bypass the ammeter and upgrading the wiring, then switch to a voltmeter to monitor the electrical system.
It sounds simple, and it really is, but does it work? Our buddy Marko X's street-brawler 340 four-speed-equipped '68 'Cuda ragtop was a textbook case for an upgrade. Still sporting its low-output, single-field charging system, now accompanied by a serious, juice-powered fuel delivery system, a high-capacity electric fan, and an MSD zap box, the stock charging system came up short, especially when this nocturnal predator was looking for victims on the streets. When the 340 was seriously overcammed and idling at 1,800 rpm, the stock charging system was able to get by. The idle speed came down to a more reasonable 1,000 rpm after a new solid lifter grind with a more conservative (by Marko's standards) 250 degrees at .050-inch cam was dropped in. At the lower rpm, however, the electrical system was in serious discharge below a fast idle. Ever look for a push start at a street race? Not good. The solution? A bolt-in swap to the late 78-amp Chrysler alternator and the attendant switch to the new-style, solid-state regulator. We performed the changeover in a couple of hours, and the problem was solved.
Our replacement '70-and-later-style,...
Our replacement '70-and-later-style, solid-state regulator that's used with the dual-field alternator sits on the MSD ignition box. Plugging wires into it requires the factory plug connector and the retaining strap. Marko hacked one out at the boneyard. The same two wires connect to the new regulator. Simply cut off the old terminals and splice them to the new connector; even the color codes are identical.
To connect the second field...
To connect the second field wire to the new alternator, tap in an extra length of wire when splicing the original blue ignition-on wire to the regulator plug. This will run to the alternator, completing the dual-field wiring. We used uninsulated crimp connectors, which we crimped and soldered, then insulated with heat shrink for a bulletproof connection.
The later-Chrysler alternator...
The later-Chrysler alternator has identical mounting points like the earlier units and bolts in on the same mounts. Some adjustability is usually lost, though, since the larger back will interfere when it swings to the inside of the stock range of travel. We learned that both big- and small-blocks lose approximately the inner one third of adjustment travel, so once you select a belt that fits, it's a done deal.