Voltage

O

Oilslickwillie

Senior Member
My volt gauge reads about 12.3 volts. Removed the alternator and new battery and took to O'Reilly's and both tested around 14.5 to 14.6 volts. Next thing I did was cleaned all ground contact points, even added ground straps from engine to frame and fender to engine. Replaced battery and alternator and checked volt gauge and it still reads about 12.3 volts. When lights, electric fan are turned on it doesn't change anything. Could it be a bad volt gauge or something else?
 
Oilslickwillie said:
My volt gauge reads about 12.3 volts. Removed the alternator and new battery and took to O'Reilly's and both tested around 14.5 to 14.6 volts. Next thing I did was cleaned all ground contact points, even added ground straps from engine to frame and fender to engine. Replaced battery and alternator and checked volt gauge and it still reads about 12.3 volts. When lights, electric fan are turned on it doesn't change anything. Could it be a bad volt gauge or something else?
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What year and model? Your '55 Fordor sedan with 302?
Are you using an aftermarket voltage gauge under the dash, or something else?
With the engine not running a voltmeter on the battery terminals should show 12.5 to 13(+) volts. With the engine running and elect. system charging, 14+ volts.
(just checking) Did you clean the spot where the negative battery cable fastens to the engine?
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After market gauge under dash. With engine running gauge shows 12.3 volts. With engine off, key on shows 12.3 volts. Battery tested out of car at O'Reilly's tested over 14 volts. I did clean cable from neg. to engine block. Also cleaned other contacts and added two ground cables, frame to engine, and engine to body. All bolt locations were cleaned to bare metal.
 
I don't know what you're using, or how the wiring is laid out, so I'll just throw this out. I've had multiple experiences with 1 wire alternator that showed 14+ volts at the output terminal, but 1-1 1/2 volts less at the battery. Depends on the length and wire gauge from the output to the battery. That's why I don't do 1 wire installs anymore. I run all three, and hook up the idiot light. That sends the actual battery voltage at the battery back to the internal regulator, and brings it up to 14+ E battery.

That said, in your case I'd try another volt gauge-yours might just read low.
 
Oilslickwillie said:
After market gauge under dash. With engine running gauge shows 12.3 volts. With engine off, key on shows 12.3 volts. Battery tested out of car at O'Reilly's tested over 14 volts.
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My first thought is the gauge or the wiring to it isn't right. Get a handheld volt/ohm meter and check the voltage on the battery terminals, running & not running.
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If you are using a GM alternator with the 2 pronged plug on the circumference of the case, the post that is counterclockwise while looking front to rear needs to be wired to a 12 volt hot post on the ignition switch or other location far from the alternator. This post is a feed-back telling the alternator how much to charge. If you omit it or connect it to a point too close to the alternator you will not indicate the true drop in voltage that exists.

The other post is the one that excites the alternator field and has to have a hot wire to it. You can just jump from the charging wire in the back to this post.

Good Luck.

If this is not the alternator you are using, forgive me for butting in. :-)
 
image.jpg
Here is a photo of my alternator. If looking front to back, the left side of plug is wired to back of alternator. The right side of plug is not used.
 
Maybe I'm confused.. From my photo, the red wire going to back post on alternator is coming from ignition switch. The left side of plug is going to this same post. Nothing on other side of plug. Do I have it wrong.
 
I haven't got a clue how to wire your alternator but...

If what Motorhead6's said in his post is describing the same type alternator as in your photo....
it's not wired right.
 
That's why I'm confused. I think I have mine wired the way Motörhead explained. Hot on ignition switch is going to back of alternator. The short wire is coming from back of alternator and connected to left side of plug. This does not seem any different than what Motörhead said except he said hot ignition wire to left side of plug and then wire from that plug point to back of alternator. My drawing shows the way I have it wired, and the dashed blue lines is what Motörhead said. Same thing since both wires are basically going from hot ignition wire to both of these locations, unless I'm not hearing it right. image.jpg
 
That looks like a GM 10/12 SI internally regulated alternator. The heavy 10 gauge minimum output wire should go to the main voltage distribution point. The two prong plug-in is labeled #1 and #2. A wire should come from the ignition switch (on) and go to #1(exciter,) and #2 (voltage sensing) should go to the main voltage distribution point, where the main output wire goes to.
The indicator lamp provides enough resistance to shut the alternator off and prevent run-on. Also lets you know if there is an internal problem.


 
This drawing doesn't look anything like how mine is wired. Mine is just wired from ignition to battery post and from battery post to #1. No indicator light.
 
Oilslickwillie said:
This drawing doesn't look anything like how mine is wired. Mine is just wired from ignition to battery post and from battery post to #1. No indicator light.
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If your alternator works fine on the O'Reilly's test bench but isn't charging the battery that's why.
Your alternator isn't wired to the car correctly.
 
Guess I could try and wire it that way. Just don't want to burn anything up. What kind of indicator light should I use. Is this light just used to excite alternator.
 
It looks like the exciter wire is missing. Do you have one from the fuse panel? This is how my GM alternator is wired up.
 

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So here is where I'm at. I have been talking to some people here in town and now I think I've gotten several different answers to my alternator question. Sometimes I get confused, but hey, I'm old and can't help it.
According to my drawing I posted earlier, here is how my car is wired:

1. Neg. post on battery to engine block for grounding.
2. Pos. post on battery to large stud on left side of starter solenoid. (also several other switch type wires, neutral safety, etc. on this same stud)
3. Wire from large stud on right side of starter solenoid to the starter.
4. Small left stud on starter solenoid is where ignition-on switch wire is located.
5. Small right stud on starter solenoid is not being used.
6. Alternator is like this: wire coming from under dash and attached to threaded stud on back of alternator. (assume coming from ignition but due to back injury, cannot get under there)
7. Pigtail wire coming from the #2 spade on top of alternator and going to threaded stud on back of alternator.
8. Volt gauge that shows 12.5 to 12.7 volts at all times. Does not change when car is running or lights turned on.
9. All grounds have been checked and bare metal contacts on them all.
10. I do not have a exciter wire as people have mentioned. Is this what I am missing, if so, how and where do I attach it?
Can I run a wire from the #1 spade on the alternator with a bulb on the end to take care of the exciter?
Also, does the above wiring seem okay but just missing an item?
11. Thanks to everyone who has tried to help me. A lot of family emergencies going on here and trying to get this thing right at the same time. I'm on the road so I hope I did not miss any ones responses.
 
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