My car is a ’62 Plymouth. It has a single field 40 amp alternator with a mechanical voltage regulator. At anything above idle the car always showed a slight charge based on the stock dash gauge. I estimate maybe 5-10 amps. I never considered it a problem. A few months ago I installed an under dash voltmeter. I was surprised to see that anything above idle the voltmeter was pegged at 16v. With the help of folks from various Mopar boards I was able to determine that I had a voltage drop of 2.5v between the battery and the ign terminal on the voltage regulator. The voltage drop was somewhere under the dash. Rather than tearing the dash apart I decided to install a relay under the hood to feed the voltage regulator. The relay is fed from a 10ga wire off the starter relay and triggered by the wire from the bulkhead that used to go directly to the voltage regulator. I started the car and the voltage at the battery is now typically between 14.6 and 14.9 depending on battery condition and about .3v less at the regulator. So far, so good. Except now there’s a new problem. The amp gauge in the dash now shows about 50% charge at anything over idle. I’m guessing this is about 20 amps. When I first start the car it shows full charge for a minute or two then drops to about half but does not go any lower.
I have checked the ground between the battery and the regulator housing. I even tried running a separate 10ga ground wire directly from the battery to the regulator mount. I’ve tried both a mechanical regulator and an electronic regulator. Same problem. Also tried two different batteries. No improvement. And out of desperation I tried a different ignition box. Also no change. I’m stumped. In the past I’ve always been able to find help on one of the Mopar boards. I hope the boards come through again. Thanks!!

How many voltmeters have you tried?
Don't rely on just one without backing up its reading with a known good one.
If you want the car to remain stock looking under the hood you'll have to dig in deeper.
Otherwise you could install a more modern alternator with built-in regulator and be done with it (aside from possible high resistance from bad connections elsewhere in the system ofcourse).

I'm not too concerned about stock appearance. I have checked the voltage with two meters. They show within .1v of each other.

How about putting a real ammeter in the circuit to see if your factory gauge is reading wrong.


Factory ammeters do not have numbers on them for a reason, they are not accurate, all they will tell you accurately is if you have current or do not have current going thru them, trying to extrapolate any kind of value beyond that is futile.

BTW, did you also make sure you had a good ground path to the alternator and regulator, both sides of the circuit have to be good.

I would seperate the bulkhead and clean the male/female terminals in both halves. I'm assuming the reg is an electronic version (most replacement ones are nowadays & if no wire wound resistors on the bottom side then it is an electronic one) & that it ain't the blue constant voltage blue reg. Jump from the batt positive post or starter relay battery post directly to the "ign" terminal on the reg. I'm assuming with your jumpering so far that the eng/reg/alt have good ground path continuity back to the batt neg post. We're the best! we'll figure it out in short order for you. You are SURE you have a good (non sulphated) batt in there? I'm thinking yes but I had to ask & the symptom (amp needle behavior) sure sounds like classic bad electromechanical reg but for it to get worse after you eliminated the voltage drops & got the charging rate back to normal ain't making sense. & the needle staying way further to the right started right after you did the mods correct? I'm not thinking a fubared field circuit path in the alt could be doing this so if the batt is good and the reg is good then it has to be a wiring (positive side) continuity issue or a ground path (negative side) continuity issue. Short version: at a fast idle what are the voltages at the (1) batt posts (2) reg "ign" terminal to batt neg post and (4) how much voltage drop on low scale (20V) from alt case to batt neg post and (5) voltage drop from reg case to batt neg post and (6) from "grn" terminal on reg to field terminal on the alt

amps don't just magically appear.

high voltage is a problem because it can damage equipment and wiring.

high amps means something is drawing that power. you cannot push 20 amps to an item, only the voltage/charge to it. it has to consume 20 amps to pull 20 amps.

So either way, as long as your voltage is good, I would say you are not "over charging" anything.

But, that amp gauge is a known failure point.
So is the bulkhead connector for charging.
IF one of those items has high resistance due to going bad, or corrosion, you may be heating something up, drawing those 20 amps.

The mad electrical bypass is what I would do next and then call it good.

BUT if you really want to trouble shoot it, rent or buy an amp meter clamp on style and see how much you are actually pulling.
or get a modern amp meter style gauge and see what it says.

Thanks for the input everyone. It may take a few days to look into all the suggestions. I will report back on what I find. I am beginning to wonder if the high amp draw could possibly be the relay I added to trigger the voltage regulator.

while it might be possible, it seems unlikely.
you can test it by putting a fuse inline and see if it is drawing unnecessary power. just toss in a 10 amp fuse and see if it pops. or 5 even.

I'm happy to see this sentence. Do yourself a huge favor, get a Denso alternator from a Toyota car or whatever, run the 2 wires that it requires, and never worry about charging problems again, it's the best thing I ever did to my big block Duster.
AR-Engineering has brackets and a pigtail for this.

read this


Charging system explained

I'm considering both the Denso alternator change and the MAD electric changes to eliminate the amp gauge from the system. Eliminating the bulkhead connector from the charge circuit makes sense to me. A more simple charge circuit without a regulator also makes sense. My concern is if I do both of those things without finding the amp draw problem won't I potentially still have a problem somewhere in the system that could result in a bigger problem?

Definitely solve the problem at hand first as you alluded to. it will fix the issue/increase your knowledge/experience/give you confidence in your abilities. Just me I like the ammeter so I do Nachos bulkhead parallel bypass to elim that weak area & clean ALL terminals/connections & I add a voltmeter to switched 12V. The Madd info is good if you dont mind loseing the ammeter function & I see the bulkhead as the problem not the ammeter itself & I strive to keep its' needle close to 12 0'clock & a person can relay the headlights/ac/heater directly to the alt. I hear the Denso is a good swap, does it use the same reg system as ours' does I'm wondering

Based on this link I assume the Denso alternator is internally regulated:
http://www.moparts.org/Tech/Archive/elec/34.html
My problem is I need a dual pulley for my application and I don't know if that exists.

Denso is a 2 wire hookup, run 2 new wires and bypass all your problems and go cruisin. Mine is always at 14 volts. And it's internally regulated. My denso was about $59 total on ebay. I have the part number at home. I just use a voltmeter, no ammeter.

Dual pulley's can be found everywhere.
I made one myself on my lathe for the Ford 3G alternator I put in my Dart.

#14611

before one can properly repair something, They first have to UNDERSTAND how it works. one can throw parts at it, BANDAID it, or understand how it works, Then repairing it becomes relatively easy.