Alternator question/problem

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jvincig01

jvincig01

10 Year
Joined
May 4, 2011
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1,465
Location
Sacramento, CA
I just put in a universal harness and have everything wired up in my 67 Fj40. However, scratching my head after testing the power.

Here is the short story...

- Brand new alternator and battery
- Odyssey battery tests fine
- GM 1 wire alternator tests fine
- Car turns over and everything is functional

PROBLEM...

When the car is running, I go to test the battery and am getting a 0.0 reading. Even revving up the engine I receive a 0.0. Shouldnt the battery be charging?

Any thoughts on what might be causing the issue?
 
Possible operator error with the multimeter? How are you testing voltage at the battery? Are you on the voltage setting (correct scale if not autorange) and testing between positive and negative terminals of the battery?
 
spotcruiser said:
Possible operator error with the multimeter? How are you testing voltage at the battery? Are you on the voltage setting (correct scale if not autorange) and testing between positive and negative terminals of the battery?
Click to expand...

I am testing at the 20v setting on DCV and testing between positive and negative terminals when car is running.
 
And you're seeing 0 volts? Are you testing it exactly as you did when you said the brand new Odyssey battery tests fine? And it cranked the engine over?

Sorry, but it seems that you must be doing something incorrectly, if you tested the battery at roughly 12.6 volts before starting the engine and now, doing exactly the same test, you see 0 volts.
 
spotcruiser said:
And you're seeing 0 volts? Are you testing it exactly as you did when you said the brand new Odyssey battery tests fine? And it cranked the engine over?

Sorry, but it seems that you must be doing something incorrectly, if you tested the battery at roughly 12.6 volts before starting the engine and now, doing exactly the same test, you see 0 volts.
Click to expand...
sorry. i mispoke. it stays at 12.6. there is no increase
 
digital volt meter, unless your meter is what's called an analog which has a meter pointer,
anyway you should be getting some kind of voltage from the battery, sounds like to me your meter
is non functional.
 
DVM is digital voltmeter. Ah, 12.6 volts makes more sense. Is this with a V8 or an F engine? How is the alternator connected? Any idea what model of alternator you have?
 
Last edited:
On some multi meters, there are 2 inputs for the positive lead. You'll use one for voltage, and one for amperage. Your reading will be 0 if you're in the amperage input.
 
Riley (@jetranger): His battery is 12.6v - it's not increasing when the engine is running - he's trying to see if the alternator is working.



Do you have an external voltage regulator? Have you tested it?

Rudi (@bj40green) helped me A LOT when my new VR (voltage regulator) wasn't allowing the alternator to fully charge the battery.

Here's the gist of what he told me... the embedded thread is great!! Adjust your VR at 2000RPM

"The VR should be in the range 13.8 to 14.8V so you need to adjust the VR. I feel comfortable with 14 to 14.2V. See my tread: Voltage Regulator (ext.) / How it works post# 14.

RPM's is more important than speed. At idle the alternator will put out only a few Amps, enough to keep your ignition going but not charging the battery. The alternator starts really charging from 1000 rpm, so if you're off road at low rpm's your alternator is not really charging. Remember.... this is 70's technology and not the "loaded with electronics and sensors" technology from today.

You have to measure the voltage on the battery.
When the battery is almost full, the VR goes from "full" to "trickle" charge.
When the battery is full the VR shuts the alternator off. Your Cruiser is now running on the battery. Slowly the voltage goes down to the point that the VR kicks in again.
This is what you see at the Voltmeter.
Adjust your VR so that you read around 14 Volts on the battery."
 
spotcruiser said:
DVM is digital voltmeter. Ah, 12.6 volts makes more sense. Is this with a V8 or an F engine? How is the alternator connected?
Click to expand...
Solace in Solitude said:
Riley (@jetranger): His battery is 12.6v - it's not increasing when the engine is running - he's trying to see if the alternator is working.



Do you have an external voltage regulator? Have you tested it?

Rudi (@bj40green) helped me A LOT when my new VR (voltage regulator) wasn't allowing the alternator to fully charge the battery.

Here's the gist of what he told me... the embedded thread is great!! Adjust your VR at 2000RPM

"The VR should be in the range 13.8 to 14.8V so you need to adjust the VR. I feel comfortable with 14 to 14.2V. See my tread: Voltage Regulator (ext.) / How it works post# 14.

RPM's is more important than speed. At idle the alternator will put out only a few Amps, enough to keep your ignition going but not charging the battery. The alternator starts really charging from 1000 rpm, so if you're off road at low rpm's your alternator is not really charging. Remember.... this is 70's technology and not the "loaded with electronics and sensors" technology from today.

You have to measure the voltage on the battery.
When the battery is almost full, the VR goes from "full" to "trickle" charge.
When the battery is full the VR shuts the alternator off. Your Cruiser is now running on the battery. Slowly the voltage goes down to the point that the VR kicks in again.
This is what you see at the Voltmeter.
Adjust your VR so that you read around 14 Volts on the battery."
Click to expand...


This is super helpful. It has a GM 1 wire with an internal regulator. It's at my inlaws an hour away so I will be checking it this weekend. You guys provided me a good checklist of things to try. Could be operator error, could be a bad internal regulator. I will report back on sunday for sure. Thanks, dudes!
 
jvincig01 said:
This is super helpful. It has a GM 1 wire with an internal regulator. It's at my inlaws an hour away so I will be checking it this weekend. You guys provided me a good checklist of things to try. Could be operator error, could be a bad internal regulator. I will report back on sunday for sure. Thanks, dudes!
Click to expand...


I'd also watch for a response from Rudi - he's in Costa Rica and probably snoozing right now. But, he'll respond when he's alerted to my earlier post... he'll probably have good suggestions for further troubleshooting.

Good luck!!
 
You've indicated the 1 wire Alternator is working, how was that determined?

Is the alternator wired per instructions? Grounded properly? Motor Grounded?

When the motor is running, is there a magnetic pull around the alternator when it is running? Does a screwdriver stick to the back of it?
 
If I am reading this again and correct you have 12.6 V at the battery. Try placing the positive lead on the lug on the back of the alt and the neg on the alt frame. What do you get there? Those one wire alts can be finicky and sometimes need to be revved up a bit to get going.
 
Don't overthink this. Just turn on the headlights when you test. You should see a difference.

www.marksoffroad.net
 
jvincig01 said:
Thanks all for the help troubleshooting. We determined it was the internal alternator regular. So we swapped in a new one and it tested perfectly!
Click to expand...

I hope you had the alternator tested before you installed the new internal regulator. The reason is that last year I installed a 80 FJ40 OEM internal regulator alternator in my 78 FJ40, after a while it stopped charging and I plugged and played a new regulator, it fixed the problem for two or three days and then stopped charging again, turned out to be alternator rectifier problems.
 
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