1979 Alternator/Voltmeter
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
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From: Gulfport MS
1979 Alternator/Voltmeter
Hi guys...decided to start up the Vette after a 4 month winter nap. The battery was initially dead and would not hold a charge...so new battery. After installing the battery the car started right up...but the voltmeter shows nothing, the GEN light is not illuminated and the voltage at the alternator read only battery power...12.4V. This 12.4V is shown at the battery terminal on the alternator and at the red wire at the plug. After stepping on the gas...and the choke kicking down to normal idle the GEN light comes on and the voltmeter reads approx. 8-9V. Now...the alternator reading is 14.3 at both red wire connections and also the white (brown) wire on the plug. Before checking voltages I swapped out the alternator with a new one (lifetime warranty)...and same results. I'm guessing the high voltage at the white wire is the problem...and I've read a few of the threads and saw mention of "the exciter circuit" which involves the white (brown). Is this my problem? And, if so...what is the exciter circuit, how does it work...and how do I go about diagnosing?
Race Director
Joined: May 2006
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"After stepping on the gas...and the choke kicking down to normal idle the GEN light comes on and the voltmeter reads approx. 8-9V. Now...the alternator reading is 14.3"
Can you clarify this statement how can you have both readings after the car is at normal idle? Where did you get the low voltage reading versus the correct reading? Is the GEN light still on with the 14.3 reading at the alternator?
Are you sure the plug with the red and brown/white wire is fully locked and doesnt have an internal wire break where the wires join the connectors? Did you try moving those wires with the volmeter hooked up?
Can you clarify this statement how can you have both readings after the car is at normal idle? Where did you get the low voltage reading versus the correct reading? Is the GEN light still on with the 14.3 reading at the alternator?
Are you sure the plug with the red and brown/white wire is fully locked and doesnt have an internal wire break where the wires join the connectors? Did you try moving those wires with the volmeter hooked up?
Race Director
Joined: Mar 2006
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From: Florida
Nothing wrong with getting 14.3v everywhere including the white wire, once the allternator is excited and charging. Gen lite shouldn't be on then.
It should drop off after a while to around 13.6v or so when the battery is charged up fully.
Just for fun, remove all the connections at the alternator and clean them up a bit. Good preventative maintenance.
It should drop off after a while to around 13.6v or so when the battery is charged up fully.
Just for fun, remove all the connections at the alternator and clean them up a bit. Good preventative maintenance.
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
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From: Gulfport MS
While the car is a fast idle...no GEN light illumination, no voltage showing across the voltmeter gauge and battery power (12.4V) showing at both red wires on alternator (almost nothing showing on the white (brown) wire).
When the choke kicks down...GEN light illuminates, 8-9V showing on the voltmeter gauge and 14.3V at all three wires (2 red & 1 white (brown)) on the alternator.
I moved the wires...and even removed the plug and replugged. Same results. I don't know what the red & white (brown) wire readings should be...although my thought is that the red should always be 14+V if the alternator is working correctly.
When the choke kicks down...GEN light illuminates, 8-9V showing on the voltmeter gauge and 14.3V at all three wires (2 red & 1 white (brown)) on the alternator.
I moved the wires...and even removed the plug and replugged. Same results. I don't know what the red & white (brown) wire readings should be...although my thought is that the red should always be 14+V if the alternator is working correctly.
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Gulfport MS
Thanks MelWff. Please excuse my ignorance...the electrical side of things always seems to confuse me.
I do have a factory shop manual...and the only diagnostics I found (from what I remember...I'm at work now) pointed to the "exciter circuit". Unfortunatley, that is as far as the dagnostics went...told me it was a problem with the "exciter circuit"...but no mention of what the "exciter circuit" is and and how it operates...or how to fix the problem. Maybe I missed something.
If the brown wire goes to the GEN light...then what is it supposed to read (when measured at the alternator) and when? I'm at work now...but, something obviously changes when the choke kicks down. Is this normal? Is the "exciter circuit" something that could cause this?
I do have a factory shop manual...and the only diagnostics I found (from what I remember...I'm at work now) pointed to the "exciter circuit". Unfortunatley, that is as far as the dagnostics went...told me it was a problem with the "exciter circuit"...but no mention of what the "exciter circuit" is and and how it operates...or how to fix the problem. Maybe I missed something.
If the brown wire goes to the GEN light...then what is it supposed to read (when measured at the alternator) and when? I'm at work now...but, something obviously changes when the choke kicks down. Is this normal? Is the "exciter circuit" something that could cause this?
Race Director
Joined: May 2006
Posts: 18,657
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this article will give you more info. The exciter circuit is the brown wire going to the GEN light. I'm surprised the factory manual doesnt have any further steps to take.
http://www.madelectrical.com/electri...hreewire.shtml
http://www.madelectrical.com/electri...hreewire.shtml
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Gulfport MS
Thanks again MelWff. After reading that I understand why reving the engine to kick the choke down changes the readings...I am "exciting" the system by spinning the alternator fast enough to turn on the regulator. But...any idea on why the regulator is not turning on on it's own? Does the white (brown) wire supply voltage to the regulator to turn it on? If so...what is responsible for sending that voltage? Everything worked fine last time I drove the car.
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