Taking Charge: Electrical and Charging Tips and Tweaks to Keep Your Mopar Current

Every 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.

wiresOur 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

bulkhead connectorMopars 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 tracks!

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 rating Wire gauge Fusible Link
Under 50 Ampere   12 16
50-65 A.  10 14
85 A. 8 12
100 - 120 A. 6 10

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.

However, 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.”

alternatorSo 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 information.

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. bulkhead connector
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.
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 forever!
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 points.
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.

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.
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 didoes in and out individually.
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 “blocks”.

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.)

15. Next, remove the three hex nuts retaining the stator-wiring lugs, and....
16. ....simply lift the stator out.
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...
18. ...remove the four screws holding the negative diode block in place. At this point, the diode assemblies basically fall out!
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!
voltage regulator20. 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.

Hemi Andersen added


For more by Rick Ehrenberg, click here!

Chrysler HeritageHistory by YearChrysler People and BiosCorporate Facts and History

We make no guarantees regarding validity or accuracy of information, predictions, or advice — see the terms of use and privacy policy. Copyright © 1994-2000, David Zatz; copyright © 2001-2017, Allpar LLC (except as noted, and press/publicity materials); all rights reserved. Dodge, Jeep, Chrysler, Ram, and Mopar are trademarks of Fiat Chrysler Automobiles.

Compass options
Leah Pritchett with Mopar Top Fuel dragster
Mopar racks up two more in Arizona

$1.8 billion FCA loan paid

More Mopar Car
and Truck News

Hot compact: Plymouth Dusters Mo-powered aircraft tug 623,000 mile Dakota

New JL Wrangler pics - now wearing less camoflageLarry and JD Power on FCA qualityTiming belt change complete, won't roll over