© 1999 Richard Ehrenberg and Harris Publications. Story and photos by
Richard Ehrenberg. Used by permission. For
more muscle car action, read 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.
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’....
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:
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.
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.”
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
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.
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.)
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.
For more by Rick Ehrenberg, click here!
Chrysler Heritage • History by Year • Chrysler People and Bios • Corporate Facts and History
More Mopar Car and Truck News
New JL Wrangler pics - now wearing less camoflage • Larry and JD Power on FCA quality • Timing belt change complete, won't roll over