Erratic voltage 1952 CJ3A - 12 volt conversion

[Kris VK]

We converted the electrical in our 1952 CJ 3A Jeep from 6V to 12V in 2015, and bought the 12V alternator kit, harness and other parts from Kaiser Willys. It's been running great since, but recently the voltage has become erratic, ranging from 8 volts to pegging the gauge above 20 volts. It holds at normal 14 volts for a while and then drops or increases when idling or when driving, without rhyme or reason. It runs very poorly when the gauge rises above 18 volts.

We removed the alternator and ran on a bench for 30 minutes and it works perfectly. I think the alternator has an internal voltage regulator. We can't locate a bad or broken wire. Our mechanic can't diagnose the issue and have the jeep back in the barn for now.

Any diagnosis ideas or advice is appreciated!

 

[Tralehead]

Have you tried a different battery?
It seems like a bad connection somewhere. Even a bad ground. There's more to finding a bad connection or wire than just visual inspection, a good digital multi meter to measure resistance is the tool to have. You should measure zero resistance between the neg post and anywhere on the Jeep. And if there's a damaged or loose plate/divider in the battery, you will never see it.
If it were me, I'd swap a known good battery in. I would also make sure I have a ground from the battery (-) to the frame, engine and body. Make sure your ground runs to the alt case as well.
Never assume you have good continuity between all those above units.
Also, how does the alt feed the battery? Does it go through any type of block or switch? Or directly to the Pos(+) cable via the starter? Check all of those connections. Remove, wire brush clean, replace tight and coat with anti-corrosive (WD-40 is fine but there are better products)

 

[Kris VK]

Thanks so much Tralehead for the suggestions! I'll check the grounds, resistance and buy a new battery to see if that resolves the issue. There is a trip switch between the Alt and the positive terminal of the battery which works.

 

[Ira]

If you're relying on the gauge to determine the voltage, it's probably important you make sure the gauge is right. Conceptually the only way you can get a voltage that high is by removing the battery from the system as it will limit the voltage to much less than 20 unless the charging current is stupidly high, the battery is disconnected or the battery is bad. If it just spikes to 20 for a second, then it's most likely a loose connection or a bad battery. I once had a bad battery in a car, it was under warranty and it was testing fine on the bench so I asked to tech to lift up the battery an inch and drop it, at that point the meter went crazy so I got a new battery, but without that it worked perfectly.

 

[Kris VK]

Replaced the battery and issue persists. Will complete measurements per Tralehead's suggestions.

 

[Blue Duck]

Just as a process of elimination, check to make sure you have a 12 volt coil and it has an internal resistor. If not internal you should have an external ballast resistor. Sometimes that gets over looked in a 12 volt conversion.

 

[Rastus]

After eliminating the gauge, check resistance & grounds of all wiring associated with the alternator & running circuit/s.

 

[Kris VK]

It does have 12 volt coil with internal resistor. I'm in process of learning how to check resistance and grounds with a meter. Replaced battery and no difference. The voltage gauge usually doesn't peg when the engine is idling, making it a challenge to test connections to determine if system is overcharging.

When driving at moderate speeds, the voltage meter will read its normal 14 - 16 volts (has always showed this reading) , and suddenly it "pegs" the gauge far beyond the max reading, and holds there. Then, when driving in gear, I turn off the key in the ignition switch, and then turn the key back into the on position, the electrical system restarts and the voltage gauge drops back to the normal 14-16 volts reading and stays there for a while. After awhile it pegs again and I switch key off/on again and it goes back to normal reading. I wonder if it fact it may be a faulty voltage gauge?

 

[Ira]

What is the volt meter? Is it possible it's faulty and there is actually no problem? Maybe try tapping it while idling.

 

[pav1]

Do you have a cigarette lighter or a 12v port?

I bought a cheapie voltmeter that plugs into my 12 v port, that way you can check voltage.

If the voltage is all over the place then could be the regulator.

Just curious are you running the new alternator through the traditional wiring and voltage regulator? That could be the issue???

 

[Blue Duck]

I would suggest use a good quality fluke meter(multi meter ) connected to the positive post on the coil and drive it to check the volts. As Pav said, you shouldn’t be running your old voltage regulator. Just for kicks, try running it with the battery disconnected, running on just the alternator. Then try running with just the battery and the alternator disconnected. It may help to isolate the problem.

 

[Ira]

It's an alternator with a built in regulator and new battery. It should be almost impossible to get 18V on that system unless the alternator is isolated from the battery somehow and it's only powering the electronics.

 

[Blue Duck]

I just checked my 2A, it is 12 volt with a 3 wire Chevy alternator. It shows 11.4 at the coil, 13.7 at the battery, and 14.0 at the alternator. The volt meter in the dash always shows 14 volts at start up then settles on about 13 volts. Can you post a couple of pictures to show how your alternator is set up?

 

[Ira]

And while I've always had Fluke meters and Tek and Pico scopes, the $6 digital meter from HB is all he needs for this and unless you're life or job depend on it or you're flush with cash, a Fluke is usually overkill.

 

[Kris VK]

Thanks everyone for so much guidance.

I found the original 6 Volt ammeter gauge in my garage, which I switched in 2015 out for a voltage gauge when we converted the jeep to 12V system. Not sure if the original ammeter gauge will work on my 12 volt system but I can try to hook that up.

There's no 12 volt outlet. We bought new 12 volt wiring harness for entire vehicle when we changed over system from 6 V. The alternator has an internal regulator. The alternator runs to a cutoff switch and then to the battery. The instrument panel harness plugs into the alternator and runs to instrument cluster.

this is the alternator kit we bought from kaiser WIllys in 2015, which included the voltage gauge

New 12 volt Conversion Alternator Kit (4 or 6 cyl) Fits 41-71 Willys and Jeep | Kaiser Willys

New 12 volt Conversion Alternator Kit (4 or 6 cyl) Fits 41-71 Willys and Jeep | Kaiser Willys

www.kaiserwillys.com

also bought complete wiring harness

New 12 volt Conversion Alternator Kit (4 or 6 cyl) Fits 41-71 Willys and Jeep | Kaiser Willys

New 12 volt Conversion Alternator Kit (4 or 6 cyl) Fits 41-71 Willys and Jeep | Kaiser Willys

www.kaiserwillys.com

I might try to hookup the old amp gauge that I still have and see if that works.

​

 

[Joe B]

Kris,
This is a long shot, but check the connections of the "S" wire shown as the blue wire in the diagram from Kaiser's instructions below.



I think this is the typical "sense" wire used in an alternator circuit to remotely sense the voltage somewhere in the electrical system and adjust the output of the alternator to maintain a predetermined output voltage at that remote spot.

Have a look here for an explanation: http://www.madelectrical.com/electricaltech/remotevoltagesensing.shtml

And have a look here for more than you ever wanted to know about charging circuits: http://www.madelectrical.com/electrical-tech.shtml


If that sense connection should disappear, I'll bet the regulator would be attempting to raise the output of the alternator trying to bring it from zero volts up to the preset voltage.


Another possibility: The regulator might be toast.

Take the alternator off and bring it to a decent autoparts store. They should be able to put it on a test jig, spin it up and test the output for you, likely at no charge.

If the internal regulator in the alternator is bad, you can usually replace those without replacing the entire alternator.

 

[Lookout Ranch]

The ammeter will be indifferent to the voltage, but any lightbulb illuminating the meter at night will not be.

 

[Joe B]

A somewhat related story about the importance of clean connections…

Had a charging problem with my 1999 TJ.

I replaced the alternator. No improvement.

Did some searching and found some reports of TJ CPU failures that caused charging problems that fit my scenario. These are due to cold solder joints on the PC board.

Sent the CPU out for service. No specific problem found.

It turned out that the contacts within the harness portion of the alternator plug were corroded and not making good connections (Duoh!)

In my defense, it was tough to see up into that plug end without pulling some of the harness anchoring. (Pretty lame excuse, huh?)

At least now I’ve got a spare alternator in my parts hoard (that I will likely never need) and a lesson that I might recall while trying to solve a future electrical mystery.

 

[airportops]

Here is another long shot - is your alternator a self exciting LOW RPM alternator? These little "tractor motors" need to be able to start making current as soon as possible to keep up with the demand.

 

[Joe B]

The alternator runs to a cutoff switch and then to the battery.

This wiring arrangement seems somewhat unconventional.

With the engine running, very briefly switch off the cutoff switch and see if the engine continues to run and if the voltmeter pegs.

That cutoff switch might be intermittent, and you may need to relocate any cutoff switch to another spot in the circuit.