Voltage Reading

QWICK6-MA

Member
Just a quick question on battery voltage.
I have a 124 amp alternator that was just installed and a brand new battery.
The scanmaster is reading only 11.8-12 volts.
Does that sound low to anyone?

Thank you in advance for your replies.
 
Voltage losses thru the wiring and depending on where the sample point is for the meter can definitely cause lower than expected volt readings.
If you or a friend has a digital volt meter is the best way to check your system as you can read right at the battery. Alternator output post or other spots to see what you really have.
Charging system voltage tends to be a little lower in warm/hot weather and a little higher in colder weather.
Normal alternator output should range from around 13.6 to 14.4 volts.
Our cars have a number of wiring deficiencies that affect various systems.
 
Though there was some debate on the thread where I got this information, I replaced the factory 12 gauge wire that goes from the alternator to the battery with battery cable size wire. Previous to doing that my scanmaster would be reading in the 12.5 to 13 volt range. Now it reads 13.5 to over 14 volts.
 
Thanks guys! Strange but I am still getting 11.8 at the battery and SM reads the same. I was a show yesterday and the gentleman I was talking to suggegested a 200 amp alt. He seemed fairly new to these cars and I did not agree that a 200 amp alt was the answer.
 
Thanks guys! Strange but I am still getting 11.8 at the battery and SM reads the same. I was a show yesterday and the gentleman I was talking to suggegested a 200 amp alt. He seemed fairly new to these cars and I did not agree that a 200 amp alt was the answer.
A 200 amp alternator will do nothing for this issue. Assuming the alternator is good and charging (check the voltage at the back of the alternator) the feed wire from the alternator to the battery may be corroded causing a high resistance connection.
 
There's a big difference between amps and volts. Think of your charging system like a faucet.

Amps are how many gallons per hour it can put out. Volts is how much pressure you have.


If your internal voltage regulator is bad, you can have a 200 million amp alternator and low voltage.


Just for kicks fire up the engine and not what the scanmaster says. Then take a volt meter and get a reading from the back of the alternator to the alternator case. Then get in the car and see how many volts are in your cigarette lighter.
 
New problem! I tested to the back of the alt and have 11.38 volts. No light with key on & engine off. Scan master reads 11.2. Car sits in the garage and nothing is corroded. I turned car off and then went to start it and will not start. New battery and alternator and now car is dead. I've been an electrician for over 30 years! I'll stick to AC wiring!
Any ideas? Even though I've owened these cares since 86, I still have s lot learn! Any more ideas? Bad alt?
Thanks in advance!
 
the small wire plugged into the alternator does 2 things, runs the volts light and feeds power to the internal circuitry in the alternator (the regulator).

if the dashboard flex circuit or bulb socket for the volts light is bad, then you will get no volts light and no charging.

Caspers has a fix for it, or you can homebrew one.

Bob
 
dash alt light went bad put algator clip from test light on alt jammed test light into good ground drove home alt chargin 14 volts help explane Bob
 
I took the cluster out to check the volt bulb. Bulb good and resistor is good. Cleaned connections on the back of the cluster and check cflex circuit board. Turned key on and volt light still did not light. Dead battery? Can't think of any other options. Caspers field fix harness? Thoughts?
 
if you have a factory alternator a non functional warning circuit will take out a perfectly working charging system. that design might be the dumbest thing GM ever did.

It sounds like you have non stock alternator (that may or may not work) so I can't say 100% that you have to have a volt light during KOEO.


It sounds like you installed a new battery with a charge and a new alternator that isn't putting out and just killed the battery troubleshooting. Based on my experience you can't get far on a full charge as these cars really suck the power. Once you get in the 10 volt range, that's it.

Where did you get the alternator?
 
Found the problem! Your not going to beleive this! I was taking the new alt. out to get it tested and low and behold the wire that plugs into the alt socket was broken! I must have done this when I put the new alt. in.
Battery charged, alt back in, started her up and what do you know, 14.2 volts and Key on volt light.
It's amazing how the smallest things give you the biggest headaches.

Thank you again for all the help from fellow members.
 
Last week I stopped a bolt on my intake swapping out a potential bad injector. Turns out I had two plug wires backwards. Silly things happen from time to time.



Pretty sure this lesson will stick with you.

Although, in your case, it would have been nice if GM didn't design a warning circuit that can kill your charging system!
 
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