Author Topic: "Full Field" Alternator Test  (Read 6631 times)

Offline Haney

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"Full Field" Alternator Test
« on: June 13, 2011 - 10:19:58 AM »
I am having a no charge issue with my 73 Cuda and have a question about testing the alternator.  To "full field" the alternator, I just unplug both field wires from the alternator and with two seperate wires take one alternator field post to the Negative side of battery and one to the positive side?  Is this right?  If the alternator is good then I should have 14+ volts at idle right?

Thanks,
1969 Barracuda Coupe, 340, 4-speed




Offline Bullitt-

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Re: "Full Field" Alternator Test
« Reply #1 on: June 13, 2011 - 08:30:37 PM »
Easier than that, just pull the green wire from the alternator & jump a ground to that terminal.
Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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Offline Haney

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Re: "Full Field" Alternator Test
« Reply #2 on: June 14, 2011 - 07:41:07 AM »
OK, I think I have a problem...  Got the trust meter out last night and with the key in the run position without the motor running I have 12 volts on both field wires on the alternator.  If I unplug either field wire, I still have 12v on both terminals.  Is this right?   I started the car and using a screwdriver, it is "magnetic" near the bearing.  Is my alternator shorted?
1969 Barracuda Coupe, 340, 4-speed

Offline Bullitt-

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Re: "Full Field" Alternator Test
« Reply #3 on: June 14, 2011 - 07:56:30 AM »
I just checked mine for magnetism and there is a light amount, my battery is not connected. The blue wire would have power in the run position so any test to ground would show power & I would think you would see power from the other terminal to ground if the blue wire is connected, if both are disconnected I would not think you would see power from the terminals but I could be wrong.
What problems are you experiencing?
Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
Screwed by Photobucket!

Offline Haney

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Re: "Full Field" Alternator Test
« Reply #4 on: June 14, 2011 - 10:01:07 AM »
I just checked mine for magnetism and there is a light amount, my battery is not connected. The blue wire would have power in the run position so any test to ground would show power & I would think you would see power from the other terminal to ground if the blue wire is connected, if both are disconnected I would not think you would see power from the terminals but I could be wrong.
What problems are you experiencing?

I don't see power when both  the blue and green are disconnected, but connect either and the other has power.    I am experienceing no charge.    I did unhook both and take a separate wire from one field terminal to Positive side of battery and another seperate wire from the other field terminal to the negative side of battery with car ideling.  Still no charge. 
1969 Barracuda Coupe, 340, 4-speed

Offline Bullitt-

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Re: "Full Field" Alternator Test
« Reply #5 on: June 14, 2011 - 02:44:23 PM »
I would take the alternator to a parts store that can spin & test.
The only alternator problem on vintage Mopars I've ever experienced was fixed with new brushes. 
Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
Screwed by Photobucket!

Offline Chryco Psycho

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Re: "Full Field" Alternator Test
« Reply #6 on: June 15, 2011 - 05:46:37 PM »
did you do what bullett suggested ?
 just short the terminal thta the green wire connects to to ground & see if the ammeter pegs , if it is magnetic it sounds like the alt is working
you will have 12v at both terminals on the field , the blue wire pushes 12v into the field & the green grounds the circuit at the voltage reg so you should read 12v at both termianls

Challenger - You`ll wish You Hadn`t

Offline Haney

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Re: "Full Field" Alternator Test
« Reply #7 on: June 16, 2011 - 07:56:43 AM »
I have been busy with work and vacation bible school at church this week.  Hope to get the alternator off tonight and checked on Friday.  Thanks for all the help!

Off subject a lot.....   Chryco, I just saw the B&B link in your sig.  So you live in Panama now?  That is cool that you have a B&B there...
1969 Barracuda Coupe, 340, 4-speed

Offline Chryco Psycho

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Re: "Full Field" Alternator Test
« Reply #8 on: June 16, 2011 - 06:05:33 PM »
let us know what you find out , you might just have a bad regulator .
 Yeah I moved to Panama , spent 32 years trying to get into the US & gave up waiting !!
If you want to get away from the cold & visit a tropical country to thaw out come down & see us !!

Challenger - You`ll wish You Hadn`t