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Taking Charge: Tips and Tweaks to Keep Your Mopar Current

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Taking Charge: Tips and Tweaks to Keep Your Mopar Current

© 1999 Richard Ehrenberg and Harris Publications. Story and photos by
Richard Ehrenberg. Used by permission.
First printed in Mopar Action

motorhead you meet knows it all. He's usually quick to offer up
his vision of the worlds best camshaft profile, intake manifold, con
rods, and the like. But turn the discussion to things electrical, and, most often, you'll get a blank stare. As the old Hemi ads said: "It's gotta be voodoo, baby."

But it's not.

Line Font Parallel Rectangle Automotive window part

Our classic, muscle-era Mopars had simple, generally reliable
electrical systems, based on the rock-solid principles laid down in
steel-reinforced concrete by Mr. Ohm and his law. But, hey,
they're now about 40 years old [updated 2014], and counting. Nothing lasts
forever, and even if it did, technology leaves it behind.

We figured the time was right (and ripe)
for us to look at some common Mopar electrical maladies, as well as a
boatload of tips, tricks, and updates. We'll touch on everything
from wiring and gauge problems, charging and starting systems, to the
latest high-tech components. We'll, for the most part, not be covering aftermarket
ignition systems, for two reasons: (1), we've done several
ignition-related stories recently, and (2) most of 'em are
supplied with good instructions. So well be sticking to the usual Mopar
stuff, but with every tip and trick we've learned in the last 40
(count 'em) years of crawling under Mopars.

We're gonna have to break this down into a couple of
installments. How many it will take is anybody's guess - the
answer is, simply, as many as we need. Charging systems are first on
the agenitals. Let's turn the key and get crankin'....

HOT WIRED: Combatting wiring harness corrosion

Product White Technology Electronic device Line
of the muscle era had generally good quality, pure-copper braided
wiring, vinyl insulation, vinyl overwrap, and pressure-crimped
connectors. The only true chronic problem appears at the firewall (bulkhead) connector. Two factors are at work here that conspire to almost insure
unreliability: Corrosion and excessive current flow. Both these
problems generally show up at the high-current-carrying points only,
and that's bad news: this can - and will - stop you dead in your

The corrosion, which doesn't stop at your quarter panels,
results from the fact that, a small black foam gasket notwithstanding,
the plug-in connections are basically open to the environment. This was
fixed on later Mopars, once and for all, by either moving the
connections inside the passenger compartment and having nothing but a
big grommet at the firewall, or using proper O-ring sealed connectors.

So what can we do about this problem? Aside from parking your car in
a nitrogen-filled environment, there's a really simple trick,
introduced by Ma Mopar in the late '70s that pretty well solves
the problem with very little effort: pack the connectors full of
grease. Full. Grease displaces air, no air, no oxygen. No
oxygen, no corrosion! But, of course, for this trick to work, any
corrosion that's there now must be carefully cleaned, and
cleaning the inside of those female connectors can be almost
impossible. While individual terminals can be swapped, in many cases a repro harness is the way to go.

The second problem is a little tougher, but solvable. There are
really only two wires that carry any serious current at the bulkhead:
the two that pass all the charging-system current through the ammeter
(on the instrument cluster.) This fatal flaw is inherent in all
Mopars built prior to 1975 (1975-1/2 for A-bodies), and, of course,
shows up more readily in cars with high-current alternators and/or
accessories. Mr. Ohm called this I2R, loss, and this equals heat,
which can cause a nasty meltdown. Chrysler's first
"fix" for this was to change to a shunt-type ammeter. In
this system, a very low-resistance element is placed in series with the
charging system in the engine compartment (built into the wiring
harness), then two wires, carrying extremely low current, pass through
the bulkhead to the ammeter. In this setup, the ammeter, though
calibrated and marked in amperes - the basic unit of current flow - is
really a very-low-voltage voltmeter. Probably, full-scale is less than one volt! This system was introduced in 1975 (midyear for A-bodies).

Even later, starting with front-drivers, Chrysler abandoned the
ammeter entirely, favoring, instead, a voltmeter. Intelligently
calibrated and understood, this works fine. If the voltage is above 13
volts at fast idle, you can be pretty sure everything's okay.
Over 15, though, and you've got a regulator problem - expect a
battery explosion if you're not careful. Under 12.5, and dropping
fast, means you'd better fix it, or call the hook - soon!

The 60s - early 70s ammeters themselves were reliable
pieces, it was the wiring that was usually to blame. If you
look any service manual of the era, you'll see that Chrysler was
well aware of the problem - in fact, police, taxi, and fleet vehicles,
whose electrical loads were typically quite high (and which vehicles
typically had a "fatter" alternator) had the two
charging-circuit conductors removed from the bulkhead connector, and
its woefully-inadequate 1/4-inch Sta-Kon connectors, and run directly
through the firewall (with a simple rubber grommet). If you've
experienced firewall connector problems, you should consider this mod
as an option.

The second plan is to convert to the '80s-'90s style
wiring. Simply connect the alternator output stud, via some serious
gauge wire (matched to your alternator's output specs) to the
battery stud on the starter relay. But be absolutely sure you splice in
an appropriate length of fusible-link wire into this new conductor!
Here's what gauges to shoot for:

Alternator output ratingWire gaugeFusible Link
Under 50 Ampere 1216
50-65 A. 1014
85 A.812
100 - 120 A.610

With this done, the bulk of the charging system current will no
longer flow through the firewall connector - or the ammeter. Obviously,
the ammeter will no longer be accurate. The plan here is a simple
accessory voltmeter, which should have its positive (+) side wired
(with practically any gauge wire) to any ignition-switched 12-volt
point, and the negative (-) side to ground.

MASTER CHARGE: Alternators and generators

Alternators for automotive were pioneered by Chrysler, and first
seen in the 1960 Valiant. Their claim to fame was that they produced
more current at lower RPM. Additionally, reliability was much improved
over the old D.C. generators for several reasons. First, the slip rings
and brushes now had to carry only an amp or two, enough to energize the
rotating field, whereas the old D.C. setup required that full output
current pass through a commutator, basically, a slip ring cut
into many segments. Without getting too scientific, let's just
say that the rotating-field alternator was a quantum leap.

Then there's circuitry: Whereas the generator required a
massive, 3-section regulator, the alternator needs only a simple single
unit. And let's not forget the very significant weight savings.

not all Mopar alternators are created equal. Early units were rated at
little as 30 ampere output ... okay for a dead-stock 1960 Valiant,
sure, but a typical late-70s heated backlight draws that much current
by itself. Add in a few kicker stereos, and the stocker is quickly
overwhelmed. Of course, Mopar responded to the need for juice in
several ways: ever-increasing current-output ratings, then a 1972
redesign, then two entirely new alternators: a massive 100 amp
(nominal, 117 max) unit in 1975, and a more compact, little-known in
unit in 90 and 120 amp versions in 1987 and (and discontinued by 1989!)
After that date, all alternators in Mopars were "purchased."

Machine Automotive engine part Engineering Clutch part Transmission part
So what about your
alternator? If you car is a restoration or restification, you'll
probably want to stay with the ubiquitous OEM-style unit (see photo at
right). But, unless you are going for concours certification, we
strongly suggest at least two upgrades: First, begin with the 1972-up
"squareback" unit; these are much more reliable than
earlier versions due to the bolt-in diode block which eliminated all
soldered connections. Second, if your car is pre- 1970, use a stock,
1970-up style "flatpack" voltage regulator. (Swapping this
into earlier cars is about a 20-minute job - see the captions below.)

If you have excessive current demands, but want to keep the stock
look, kits are available for swapping the stator windings and diode
packs to beefier versions, increasing the output to 80 amps. We found 4
versions of these kits in the J.C. Whitney catalog (!), including crazy
105 ampere versions and press-in diode versions for the
pain-in-the-neck 1960-71 alternators; installation is covered in
figures 12 thru 19. But be forewarned: if you make this swap, all charging-system wiring and connectors must be up to the task, including fusing, as outlined in the first section of this work. This caveat applies to any changes you make to charging system capacity!

You could also swap in the later Chrysler-built alternators, we
advise against it. The 100-amp unit is a heavy beast requiring special
brackets, and while the later one is viable (V-belt pulley is
available) but still not the easiest one to deal with since it's
almost a one-off piece. The best alternator swap is the small, light,
Japanese Nintendo (okay, Nippondenso) unit that was phased in during
the late 1980s. While radically different at first glance, a closer
inspection will reveal some similarities. See photos 10 and 11 for swap

Photos and easy update instructions

1. Bulkhead (firewall) are the universal trouble spot. Left,
connector used on '71-'74 B-bodies and all E-bodies.
Charging system current (to ammeter) typically utilizes cavities 16 and
18. On pre-'70 B-bodies and '67-mid-'75 A-bodies,
ammeter current is typically via cavities J and P. These are the
trouble spots. Note that on fleet vehicles, the factory wisely routed
charging though a solid wire passed through a grommeted hole in the
firewall, eliminating the trouble spot.

Product White Technology Electronic device Line

Still life photography Steel Silver

3. Here's where those firewall wires terminate - the ammeter
on the instrument cluster. Notice how beefy the studs and wiring are.
Wouldn't it be lovely if the bulkhead connector was this good?
Notice that the "black" (negative) side of the ammeter was
the factory's choice for accessory current take-off.

4. To straighten out the wiring problem permanently,
you need some decent supplies. A few feet of automotive-grade wire, 10
or 12 gauge (depending on you alternator's rating and anticipated
current loading), fusible links (see text), some crimp splices and
heat-shrink tubing, and, if need be, some quality electrical tape. If
you're adding any other accessories, do yourself a favor and opt
for the modern blade-type fuse holder and fuses.

Black-and-white Monochrome photography Body piercing Wrinkle Nickel

5. Connect a fusible link to the starter relay stud. Crimp-splice
in a piece of suitable (heavy-gauge) wire, and connect the other end to
the alternator stud. That's it....firewall problems bypassed

Monochrome Safety glove Monochrome photography Black-and-white Leather

6. Still, you should repair the bulkhead connector. While
reliability is now much improved (since charging current is no longer
routed through the firewall, and, effectively, two cavities are
paralleled), some current still flows here. Begin by pulling all male
lugs out as far as possible, paying special attention to the heavy-wire

Monochrome Monochrome photography Black-and-white Leather Wrinkle

7. Then clean the terminals. A small wire brush is good for the male ends, about all you can do with the females is spray some contact
cleaner in. Then pack everything liberally with grease and reconnect.
It also doesn't hurt to manually seat each male lug by shoving a
small pin punch through the back of the insulator.

8. Fairy common is the huge 100 amp Chrysler (Indy)
built alternator which was available from 1975 through approx 1987.
Rugged, reliable, heavy. Not easy to swap - requires special bracketry
and shock-mounting.

9. Rare, but quite good, was the Chrysler-built 90 to 120 amp unit seen below.
It's no larger than the old-style 30-65 amp units. Still,
it's oddball enough that we can't recommend it. Offered
from 1987-'89 only; V-belt pulley available.

Machine Automotive engine part Engineering Clutch part Transmission part

10. The late-model Nipondenso alternators (left) can be
retrofitted. Mounting is basically similar. Stud (not called out in
pix) is used instead of Indy-built (right) unit's 5/16" threaded
hole for tensioning bracket, but this is of little consequence. Pulley
bolts on and is easily replaced or swapped on ND unit. Wiring is easy
(see photo 8.) Biggest hassle is extra depth (thickness.) In most
cases, it still fits, but output stud must be shortened and insulator
(to splash shield) discarded. To prevent potential major-league short
circuits, simply cut away the splash shield as needed.

11. To wire the ND unit, simple swap your stock push-on field lugs for some ring-type terminals. Crimp securely.

Font Gear Black-and-white Machine Circle

12. To uprate and upgrade the familiar Chrysler alternator, we used
this kit from J.C. Whitney. This one is for '72-up units and is
rated 80 A., stock number is 73GA7541Y. The 80 A. kit for pre-1972
alternators is 73GA7540P, but it requires soldering and pressing the
diodes in and out individually.

White Black-and-white Monochrome Circle Silver

13. The common Chrysler-Indy built alternator of the
'60s and '70s was simple and straightforward. The 1972
redesign improved on an already good design by eliminating soldered
connections and by mounting the diodes on a pair of simple-to-replace

Transmission part Drawing Aircraft Automotive engine part

14. Installation requires only simple hand tools - a few 1/4"-drive
sockets. Begin by removing the brushes (don't lose the special
insulating hardware) and thru-bolts, then simply pry the case halves
apart. Keep the stator with the rear (brush) half. All modifications
are done to this half (left in this picture.)

Black-and-white Circle Monochrome photography Monochrome Nail

15. Next, remove the three hex nuts retaining the stator-wiring lugs, and....

Circle Black-and-white Still life photography Monochrome Monochrome photography

16. ....simply lift the stator out.

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17. Remove both nuts (one shown here with socket wrench on
it, and one on outside, on output stud,) and all insulating hardware
(will be obvious). Also remove the capacitor. Then, from the outside...

Sculpture Black-and-white Monochrome photography Ancient history Artifact

18. ...remove the four screws holding the negative diode block in place. At this point, the diode assemblies basically fall out!

Black-and-white Auto part Monochrome photography Circle Monochrome

19. Reassembly is the exact opposite of disassembly, with just two caution spots. One, be certain that the thin mica washer (shown here) is in place. Two, do not tighten
the negative diodes screws (4, photo 18) until all other diode hardware
is installed and tightened. Also, a daub of fresh high-temp grease
wouldn't hurt the needle bearing!

White Line Technology Font Black-and-white
Flat-pack style electronic regulator is cheap and reliable. Virtually a
must! To use it, you need any alternator with two field terminals, and
the connector itself which is an easy junkyard score, or can still be
had new as of 2013. Simply splice the connector, wire-color for
wire-color, to the existing (old) regulator pigtails. Then simply
splice in one more blue wire which you then run over to the second
alternator field terminal. (If you've been using a later
2-field-terminal alternator with a pre-'70 regulator, the
second terminal would have been grounded through a short jumper wire -
remove the jumper, naturally.) That's all there is to it! And you
waited 25 years?

21. Charging-system schematic illustrates the simple differences
between the old and new-style regulator wiring. Okay, you're
scared of electric stuff. But this is s-o-o-o simple, Vern.

Text White Line Font Black

Hemi Andersen added

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For more by Rick Ehrenberg, click here!

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