The alternator case should be less than 1Ω to body and battery grounds. The negative battery terminal should also be less than 1Ω to body and engine grounds. You have poor grounds.
You mention a battery-to-frame-to-body ground. Are there engine-to-body and engine-to-battery grounds? It is important not to skimp on return paths between all components. Relying on current to pass through one component to get to another component will be a high-resistance path back to the battery and may create 'ground loops'.
The voltage regulator case also needs a clean and tight ground. I have also pinched the v/reg terminals closed slightly with pliers to make better field circuit contact.
Headlamp switch and socket terminals may be 'tarnished', making a high-resistance circuit. Even a 1 volt drop in the circuit will noticeably dim lighting. Sometimes unplugging and re-plugging in connectors a few times will 'scratch' in a better contact.
Is the radiator core support and front fenders securely bolted to each other and the car body? Are the headlamp ground terminals using clean screws and sheetmetal?
Sometimes corrosion can hide under a screw head or battery terminal and look fine from the outside. Scrape the paint away under the terminal so you have a metal-to-metal junction.
Idle speed and alternator pulley size can also affect alternator output.

 

Here's another issue:

You are using 6 AWG cable from the alternator to the battery.

You need 0 AWG with that long a run of cable. You are creating too much of a voltage drop due to the resistance of the 6 AWG cable.

 

Sorry, I was mistaken on the resistance readings regarding the grounds. I thought I had checked them with the multimeter on the 20k ohm setting, but I actually used the 200 ohm setting. Those values are not 300 and 600 ohms, they are actually 0.3 and 0.6 ohms.

Also, the wire from the battery (in the trunk) to the starter relay (under the hood) is 0 AWG wire, the 6 AWG jumper goes from the alternator output to the starter relay where the 0 AWG wire from the battery connects. I installed the 6 AWG jumper along with the 90 amp alternator because I did not want all that current going through the bulkhead connector.

I am running a ground strap from the engine to the body; I do not have a ground going directly from the engine to the battery since the battery is in the trunk. When I checked the alternator ground and voltage regulator ground (also 0.3 ohms), I had one lead of the multimeter touching the component in question and used one of my hood pins as the contact point for the other lead.

I notice that the reading on my voltmeter (it is an aftermarket unit I installed) seems to fluctuate some at idle in gear; Could my somewhat lopey idle (from the aftermarket cam) be causing this?

 

If you're still running a stock ammeter on that Duster then all charging current runs through it. That means that all current runs through the firewall connector twice, in and out. That connector is a notorious trouble spot. Check it first. And then run a 10 gauge wire from the alternator to the ammeter and back to the battery cable. Better yet, replace the ammeter with a voltmeter and run the 10 gauge alternator output straight to the battery cable.

 

Better yet, replace the ammeter with a voltmeter and run the 10 gauge alternator output straight to the battery cable.

Vintage Chrysler electrical repairs and updates

Simple, its nothing thats wrong...
the alternator doesent charge enough at low idle, its spinning to sloowly.

With an older design that doesn't work well there. Dan Stern told me, if I don't like that, I need a more modern style alternator. I can't recall his specific advice on which one to get but can look it up.

The 70's mopars I've owned all acted similar to yours when at a stoplight. They showed a negative 10 amps [headlights on- fan on high]. As soon as I took off, the ammeter would read positive ~ 10 amps and drop down to ~ 0 amps after a few minutes. This is with a 35 amp alternator. Normal stuff.

Yes.... I have that issue on my car as well and have had it on every classic Mopar I've ever owned, from the base 35 amp units up to the 1976 taxi/police V8-A/C unit.

 

Simple, its nothing thats wrong...
the alternator doesent charge enough at low idle, its spinning to sloowly.
Either live with it or get pulleys that spins the alternator faster.
Lareger wires wont hurt either but it wont completely solve the problem. They probably did this even when new.

 

Bulkhead (firewall) connectors were problematic on many of these. Melted plastic from high-resistance heat on current carrying terminals was an issue. Brass or tinned-copper terminals were the best conductors, but the brass oxidized after awhile and became a poor connection.
A smaller alternator or larger crankshaft pulley will spin the alternator faster and increase output at idle.

 

KOG, I do have an aftermarket voltmeter connected in parallel to the stock ammeter. The 6 AWG wire I mentioned above connects the alternator output directly to the positive battery cable at the starter relay.

 

Well, you've already dodged the biggest bullet on A body charging systems in that case.

 

Where would I go about getting a larger crank pulley or smaller alternator pulley? I didn't think the 90 amp nippondenso truck alternator would have this problem......

 

The 70's mopars I've owned all acted similar to yours when at a stoplight. They showed a negative 10 amps [headlights on- fan on high]. As soon as I took off, the ammeter would read positive ~ 10 amps and drop down to ~ 0 amps after a few minutes. This is with a 35 amp alternator. Normal stuff.

Truck pulleys seem larger than car pulleys? Also, if one diode failed, the result would be lowered output.

 

You don't get necessarily get full voltage charging at idle. A fully charged 'good' battery should produce 12.2 to 12.5 volts for 15 to 20 minutes depending on the load. So... dim lights at idle suggests either a weak battery, dirty connections, or a bad ground. I have had batteries that start an engine with no problem, but had one weak cell that you could only identify by dim lights at idle when the alternator can't turn fast enough to produce adequate charging voltage.

 

I repeat ...this is nothing wrong.
They can build it so the alternator charge well at idle in drive but then they would have greater parasitic losses and more wear and tear at Cruise.
It really doesent depend of the size of the alternator, its the speed of the rotor through the magnetic field in the alternator that have to be high enough
to reach the needed voltage.( this speed is a design choice when manufacturing the alternator.)
- its all about optimisation and not charging at idle in gear is an easy trade off.

 

So I think I found the "problem." It looks like AC TC is right on with the pulley ratios being the culprit. The crank pulley on my big block measures ~6 1/2" in diameter; I compared this against a '89 318 crank pulley I have and it measures 7 1/4. So it looks like later engines with fuel injection and more electronics used a larger diameter crank pulley to spin the alternator faster to meet the greater current demand. I am not sure if the larger crank pulley will even clear my water pump pulley, and even if it will I don't necessarily want to deal with the added parasitic loss. I think for now I will maybe just bump my idle speed up slightly to compensate.

 

It sounds like you have found your problem. When you are looking for bad grounds an ohmmeter is not the most reliable method, they usually have a little nine volt battery that sends current through the connection to get an ohm reading, in larger connections like you are measuring that is not reliable. Use voltage drop on both the positive and negative side of the circuit, that way you have a live circuit and it will tell you exactly what is going on. You want as close to zero on both sides of the circuit.

 

I've been told that cheap ammeter's in the 70's and earlier vehicles can often go bad and draw a lot of current off the charging circuit. (remember, in this era they were only designing cars to last 3 years) I don't know how true that is, but you might note most vehicles, if they come with some sort of gauge for the electrical system anymore, they come with a voltmeter.

Headlights dimming a bit while at idle is pretty common in 70's and earlier vehicles, like mentioned. Its a matter of how severe it is, as to if something is wrong. Again a voltmeter is probably more helpful than ammeter in this case. When at idle, the alternator is clearly not spinning fast enough to meet the current draw of the vehicle, this will cause the voltage to drop, but as soon as the voltage drops to the same as the battery, the battery will start helping the alternator by providing current along with the alternator. In these charging systems the battery is needed for far more than just starting the vehicle, they are also an electrical reservoir to aid the alternator when needed. So if you're battery is NOT in good shape or the cables and connections to the battery are NOT good either, then your headlight dimming will be worse.

With a voltmeter, you can tell what the battery voltage is, it will be the voltage that the voltmeter drops to when you first go to idle, and if the system can hold 12 Volts or better while you're idling for up to a few minutes, that seems like a normal system to me. If the system is dropping below 11 Volts right away or after a minute or two, then off hand I'd say its weak, and it could be wiring, alternator or the battery.

Don't forget battery cables can go bad, especially 35 year old battery cables. Their condition can be deceiving, since the battery cable has to flow an incredible amount of current when starting, I've seen battery cables pass most typical checks with multi-meters that flow pico-amps through it to check, but can't flow the 350 amps for starting. Stuff like corrosion, the lead terminals to copper wire connection loosening or corrosion forming in between, stands on the copper cable breaking. Cleaning the terminals on the cables and battery never hurts and often helps a lot more than you would expect.

Oh, a bigger diameter pulley on the "Engine Crankshaft" should spin the alternator faster. A bigger diameter pulley on the "Alternator Shaft" should spin the alternator slower. Not sure if you're were talking about a bigger pulley on the engine crank or the alternator shaft, it seems like we are sending confusing messages on the pulley diameters.

 

Good points raised there. I found the problem much less annoying with a new battery. The cables do go bad and good luck finding them for a vintage car - some are around and some are not.

 

The diameters I mentioned are indeed for the crankshaft pulley. The crank pulley I have on the engine now is a single groove and measures 6 1/2." I have some parts from an '89 318 TBI engine in my garage, including the crank pulley. That crank pulley is a 4 groove pulley and it is 7 1/4." The water pump pulley appears to be a smaller diameter on the 318 than on my 400 also. My guess is that this prevents voltage drop at idle for the TBI engine and also improves cooling (bigger crank pulley, smaller water pump pulley).

In all fairness, dropping down to battery voltage in my situation is annoying, but the only things really drawing current are the heater, headlights and electronic ignition. The battery alone can power those things for quite a while. I had the field windings lose continuity on an alternator a while back and I limped it nearly 10 miles back home with the alternator not functioning at all.

 

In all fairness, dropping down to battery voltage in my situation is annoying, but the only things really drawing current are the heater, headlights and electronic ignition. The battery alone can power those things for quite a while. I had the field windings lose continuity on an alternator a while back and I limped it nearly 10 miles back home with the alternator not functioning at all.

Heater? You have an electric heater? Or are you saying the blower fan for the heater core?

The headlamps draw a lot of current, electric heaters (which window defrost often is) and blower fans also draw quite a bit of current. The electronic ignition, not so much.

Again, you have to look at the actual voltage the whole system drops too when the engine is at idle. A weak battery (and other things wrong in the electric system could make the battery appear weak or actually be weak) will let the voltage drop much lower than 12 Volts and that would make for a bad diming of the headlights.

Dimming headlights in this era vehicle is normal, its subjective to how annoying that is. Checking and tracking the voltage when the engine goes to idle and is using the battery to supplement the current draw, will tell you if its normal or something is wrong.

If the electric system is working like it is designed, than you either have to live with the annoyance or change the design. Like someone suggested before, retro-fit a modern alternator to your vehicle, won't be cheap or easy, it may NOT be reliable either, but it likely will solve the annoyance of dimming headlamps.

Another alternative, if the electric system is working properly, look into some new types of LED headlamps. LED likely will draw a fraction of the current of the current incandescent bulbs used in the headlamps and might avoid the dimming at idle.

 

I've found Chrysler ammeters of the 70's to be dependable. However, the nuts on the back got loose with age or weren't torqued enough at the factory. This resulted in excessive heat which melted the plastic housing in some of the trucks. [and electrical problems.]

Cars/trucks back then lasted 100,000 miles or so. There were a few exceptions. And, during those years, cars were shuffled thru auctions and the true mileage got 'modified'. The trend back then was to buy a new car every few years. Because cars looked different due to styling changes most every year, your friends would know you were driving an 'old car'.

The old Acclaim didn't dim its lights much at a stop light. But it had a smaller alternator pulley [serpentine belt].

 

Yes and it wasn't just a poor connection at the ammeter gauge nuts. The entire electrical load of the vehicle had to pass from the engine compartment, though the firewall (bulkhead connector), through the ammeter (and its parallel shunt) and then back to the engine compartment.
There was a lot that could go wrong here in the way of something causing a high resistance, especially with age and oxidized terminals. It could also be intermittent.
High resistance with a high load can cause intense heat. Ignition switch, headlamps, rear window defogger and heater motors pass a lot of current that can melt plastic connectors and wiring.
The automakers couldn't get away with having such a fire hazard these days.
The OP has apparently bypassed his ammeter (current flow meter) and is using a voltmeter as a charging indicator?

 

I think the OP said he added a voltmeter and kept the ammeter. Which means he has an additional tool to access the state of the electrical system, but didn't rectify the problem "IF" the problem is the ammeter.

Hmmm, to further what IC said;
An Ammeter has to be inline with the entire circuit to read the current flow, and all the current running through the circuit runs through it.
A Voltmeter just has to tap anywhere on the circuit to ground to read the voltage at that point, the amount of current flowing through it is very low.

So an Ammeter you have big main cable from the battery and alternator rerouted to run through a cheap plastic gauge in the dash (plus all the other connectors IC spoke of), hmmmmm, lots of things to go wrong there that effects everything in the electric system....
But a Voltmeter, depending on what wires are already running under the dash, you can just tap one to go to the voltmeter, there will be more than one wire under the dash that will be the same voltage potential as the main cable from the alternator/battery. If something goes wrong, its only effecting that tiny tap that can be fused to prevent a short.

Another way to look at it, the water flow through a pipe analogy.
A voltmeter is just a pressure gauge, any of the pipes that are at the same pressure as the water main that are nearby, you can tap a tiny hole for a pressure gauge, and have a good idea the pressure of the water main, something goes wrong, you're only losing what can go out that tiny hole for the pressure gauge.
An ammeter is a flow gauge, so its got to be inline in the entire water main itself, so to put it on the dash, you have to run the water main up under the dash and back, and if something goes wrong the entire water main is compromised.

My guess, back then so few drivers understood electricity well enough, that an ammeter that could simply show if the battery was charging or draining, was a benefit, a voltmeter would be utter useless to most drivers.
Might explain why since the technology became cheap enough in the 80's/90's, just about every vehicle went to digital processor that simply monitored and lit a Warning Lamp on the dash if there was something a voltmeter or ammeter would show as bad. Not to mention they monitor the field control of the alternator, and can warn of things even the most knowledgeable driver could miss with just a gauge.

Personally, I think a Voltmeter is more valuable, "IF" you understand enough about electricity to understand what its telling you.
I'm sure designers, when giving the challenge that the vehicles had to last longer and be more reliable, realized the way they were doing ammeters had to go. There are ways to do it more reliably, but they're not cheap, as well, for most drivers, the warning lamp that cost even less than the gauge was probably more valuable and reliable.

 

You don't need to run all the current through an ammeter to get a reading. An ammeter shunt is a strip of metal with a known resistance, where there are two leads connected to your gauge. The gauge is actually a voltmeter reading the voltage drop across the strip of metal, however the gauge is calibrated to read amps . You can make your own shunt with a piece of scrap metal provided your have an ammeter to calibrated it with.

Datcon-Datcon - Shunts For Ammeters, 300 Amps - 07618-00-07618-00

 

The ammeter held out for WAY too long, but it was very good at being perfectly clear about what was going on.

I still havent' replaced mine but it's on the long list. In a Valiant, with a steel dash, it's a real pain to get to, though.

 

The ammeter held out for WAY too long, but it was very good at being perfectly clear about what was going on . . .

I think it is interesting that Chrysler had equipped all vehicles produced starting in 1961 and later (probably through the 1970s) with ammeters but the labeling indicated the word ALTERNATOR. Ford and Chevrolet had been using an idiot light for generator charging for many years before and continued even after adopting alternators in 1965 and 1963 respectively. Chrysler advertising in 1961 touted the advantages of the only manufacturer using an alternator to keep a better charge on the battery. I wonder if using an ammeter named alternator was a marketing decision to exploit an engineering advantage?

The driver would have to know how to interpret the ammeter gauge. You start the engine and for a short time of a few minutes the needle would be significantly moved to the right indicating a high charge rate. This was necessary to quickly replenish the battery after engine starting. After a few minutes and when the battery reached full charge the regulator would diminish the charge and the needle would hover around the midpoint indicating no charge or very little. If the driver did not know that his was normal, some could say the needle moving to center was indicating a problem.

 

I don’t think there’s a lot of knowledge to gain — you pretty much described it. And I think you are on to something with the reason for using ammeters. We even called it “the alternator gauge” though in fairness we didn’t call the coolant temperature gauge a coolant temperature gauge... it was just a temperature gauge. The alternator gauge told you about what the alternator was doing.

The use of an ammeter really hurt efficiency...

 

[sigh] I will wait

 

Wasn’t aware you could tilt the panel out since it’s all fastened to the dash. That would be a lot easier than lying on my back and working upside down.

 

Put in LED bulbs like I did, for 99 cents each, and never have to replace them again.

 

I have two motorcycles in which the alternators have permanent magnet rotors.
Dont produce much at idle but at about 3k it comes on in a rush.

 

Stovebolt Tech Tip -- Antique Chevy / GMC Truck Restoration Help

I might try this next summer