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1979 alternator not charging

 
Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/15/13 06:00 PM

I have a 79 fox body with a 289. Carburetor is a2 barrel with electric choke. I am having a problem getting the alternator to charge the battery. I am getting a reading of battery voltage when checking charge status. No charge. I took the alternator to auto zone and had it tested. It tested ok. But the diode test reading was N/A. The battery post on alternator is connected to the battery wire. The fld wire was connected to the F on the voltage regulator, and had a diode connected  in line between fld alternator and f on voltage regulator. The sta on alternator is connected to the s on voltage regulator. I replaced the voltage regulator, and had no change. Can not get it to charge.  What am I doing wrong? Is there another testing procedure to check the status of the problem? Any help is greatly appreciated.. Confused  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/15/13 09:01 PM

85 V6 Mustangchargingsystem Zpsb11e2899

this is kinda rough....

first... this diagram is for an 85.. but the system and the colors are probably the same..

do you own a digital volt meter..?? decent ones can be hand for just over 20 bucks. but a 5 or 7 buck one will work..

you might want to with the engine off..   disconnect the battery...   count the wires on the battery positive side of the starter relay on the inner fender..

then remove the nut holding the battery cable and other power wires on the solenoid stud.  wire brush both sides of all the ring terminals and the threaded stud.. then reassemble. count the wires again to verify...

now... reinstall the battery.. lets check the system..

this is printable...  run it...
~~~~~~~

Voltagedroptesting

~~~~~~~~~~~

post results..


back to the alternator wiring...

A.    do you have full battery voltage at the output terminal on the back of the alternator..  shows as a black and orange wire in the diagram...???

B.    on the regulator connector A terminal.. do you have full battery voltage??? this is usually a yellow wire...

C   on the regulator connector I terminal..  do you have power when you turn the key ON.. not full battery voltage but close..  this is usually a green and red stripe wire..  this indicates the alternator light in the dash board is getting proper voltage from the ignition switch..


D..  now... with the voltage regulator UNPLUGGED..  the digital volt meter set to 20 volts DC.. and the engine running...      with a short section of wire.. for a few seconds..  jump the F to A terminal on the connector removed from the regulator...  you will have to rev the engine to see if the alternator is working at max field.. please don't go over 15 volts.. just pull the wire.. or drop the engine back to idle..  

if the voltage goes up to or over 15 volts. thats good...

but lets do one more check...

E.     move the volt meter over to the S terminal on the connector removed from the regulator.. change the setting to 20 or 200 volts AC... leave the negative test lead connected to the negative battery...     jump the F to A again and see if you get exactly half the charging voltage in AC.. if you get AC VOLTAGE ON THE S TERMINAL..   But the charging voltage does not increase.. the diodes are blown out..

***    this replaces the E test above..    set digital volt meter to continuity beep or 200 OHM setting..    run continuity test between STA on back of the alternator and the S terminal on the regulator connector... this proves that the brittle wire with cheep connectors is bad...

G.. same test.. .. between the F terminal on the regulator connector and the FLD on the back of the alternator...


~~~~~~~~~~~~~~~~~~~~

how it all works..    the I terminal turns on the regulator...

the A terminal connects the regulator to the positive battery...

the S terminal comes from the STA on the alternator.. this is A/C voltage to vibrate the contacts in the regulator to keep it charging at the proper rate depending on the speed of the alternator..

the F terminal. the voltage regulator pulses positive current to the F terminal and to the FLD .. this goes to one of the brushes inside.. the other is grounded.. this creates a variable size rotating magnetic field inside the stator windings..  

if you connected the FLD to positive and then brought the engine rpms up.. it should MAX field.. and will COOK the battery with around 19 or 20 volts within a few minutes..

Ford Alternator 7078 1G Rear

80 Salternator  

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MustangMan
Moderator
Posts: 259
Joined: 08/11
Posted: 07/16/13 06:54 AM

As usual Wayne has some great info. One thing I want to add, you might not have any power at the I terminal on the external regulator to turn on the system. This is called the exciter wire and comes from the ignition switch through your gauge cluster's battery/charging light. If the light is burned out a 470 ohm resistor is supposed to supplant the burned out bulb and allow the exciter wire to still do its job. If your cluster is damaged, the resistor bad, or perhaps you built a custom cluster with aftermarket gauges,who knows. But what you can easily do with your volt meter or even a test light is to verify you have power at the regulator's I terminal with the key on. If you do not your charging system is not going to do squat.

Check that as well and report back.

HTH...
Mark
.  
Mark Houlahan
Brand Manager
Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto
2005 F-150 4x2 4.2L V-6/4R70W Auto

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/16/13 07:11 AM

Thank you mark and Wayne for your information. I am going to check all mentioned. And will get back this evening with the results. From what I remember, there was no I wire coming from the connector on voltage regulator.  

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/16/13 10:15 AM

Ok guys, I checked as mentioned. And this is what I found.

Under Voltage drop testing:
1. 12.8 DC volts was the reading. About the same a battery.
2. .01 Dc volts
3. .11 DC volts
4. .14 DC volts

Back to the alternator:
A. yes
B. yes
C. Has no I connector on harness at regulator
D. over 15 DC volts
E. 16.7 AC volts
*** replaces the E test: .3 ohms
G. about .3 ohms

When measuring resistance between F of harness at regulator and fld on alternator. It showed an open circuit because of the inline diode(installed before I got the car). When I checked it on diode test,with the positive probe of meter on the f prong of harness at regulator, and the negative probe on fld of alternator,the reading was 570's and dropped to 543. If I reversed the probes, I got no reading on diode test.

   Still not charging. Any information on what I should check next?  Confused  Thank you so much for you information. I am taking note and learning..you guys are the bomb!  Wink  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/16/13 12:07 PM

Under Voltage drop testing:
1. 12.8 DC volts was the reading. About the same a battery.
2. .01 Dc volts
3. .11 DC volts clean and repair the battery to body connectors around the engine bay.
4. .14 DC volts  clean and repair or replace the braided strap between the back of the engine and the firewall..



Back to the alternator:
A. yes
B. yes
C. Has no I connector on harness at regulator  without an I wire. you probably have an amp meter instead of a light..
D. over 15 DC volts.   this shows that the charging system is capable of putting out current..

E. 16.7 AC volts    this is strange.. i did not expect this much AC voltage..  normally i find about 1/2 the actual charging voltage..  this is kinda indicating that the diodes may not be working properly..  as its taking a LOT of forward current to push thru them...
*** replaces the E test: .3 ohms
G. about .3 ohms

When measuring resistance between F of harness at regulator and fld on alternator. It showed an open circuit because of the inline diode(installed before I got the car). When I checked it on diode test,with the positive probe of meter on the f prong of harness at regulator, and the negative probe on fld of alternator,the reading was 570's and dropped to 543. If I reversed the probes, I got no reading on diode test.

i really don't know of any reason for there to be a diode in this circuit..

can you create a jumper and bridge around the diode going all the way from the F terminal to the FLD on the back of the alternator for a test..



  Still not charging. Any information on what I should check next?    Thank you so much for you information. I am taking note and learning..you guys are the bomb!    


a few more voltage drop tests..

H.  alternator output terminal. to the battery positive...

I.  voltage regulator A terminal.. should have power come on with the ignition switch.  then do a voltage drop test .. from the yellow A wire to the battery positive..

J.  alternator case.. to the voltage regulator case...  voltage drop..

i will have to go study the wiring diagram for the 79 model year...

belt tension check...  with thumb.. does the alternator pulley slip when you give it the thumb test???


run the tests if you are around and post them.. i might have more before you get back...

were you able to take the wires off the starter relay.. and wire brush both sides of the ring terminals???  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/16/13 12:21 PM

oh... do a voltage measurement from the output stud on the alternator to the rear case of the alternator.. with the meter set to AC VOLTAGE..   you should get less than 0.02 volts AC as i recall..  

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/16/13 03:52 PM

Ok, went back to #3 - clean and repair, new reading .02
                #4 - clean and repair, new reading .04
                E - Now 15  As far as diode bypassed and did no good
                H - alternator output  12.7 about the same as battery
                I - voltage regulator  01-02
                J - alternator case .01
                    alternator pulley slip when given thumb test? - good

                Also, on back to the alternator wiring. on E. You had mentioned"jump the F to A again and see if you get exactly half the charging voltage in AC.. if you get AC VOLTAGE ON THE S TERMINAL..   But the charging voltage does not increase.. the diodes are blown out.."  What diodes are you talking about? I dont think the alternator has diodes.. At least the auto zone man tested it. And the test indicated N/A on diodes. He told me the alternator did not have them? That was probably why there was a diode in line.

Read more: http://forums.mustangmonthly.com/70/9464276/1979-1993-mustangs/1979-alternator-not-charging/#ixzz2ZFn5kiKa


                Did get all ring terminals brushed brushed.Just measured the AC voltage from output post on alternator to case. got a 27 VAC reading. WOW.Much higher than the .02 I was looking for. I am sure it is an indicator for something.LOL.

 Still no charge.. Confused  I had failed to mention I just bought this car from a fellow who was gonna attempt to turn it into a drag car.LOL... He said just put a battery and a radiator hose on it and it should run. Well... after rebuilding the the 2 barrel,(not to mention the other little things) and trying to get it to crank, I realized the neutral saftey switch was half unplugged.he had already pulled the dash board out. The wire plugs for it still look in tack. I guess he was gonna put gauges in. Well he also for some reason pulled the steering column covers off and slightly unplugged the switch. Now it is running, but will not charge.  

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54packman
Enthusiast
Posts: 342
Joined: 11/09
Posted: 07/16/13 04:44 PM

try connecting a the test light between the pos. terminal of the battery and the i terminal, us it as the alt light, and see if it will charge then. if so you know its in the alt light circuit, does the alt light come on at all with the ignition?  

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/16/13 05:04 PM

Sounds like a good idea. will try it in the AM.(If I can wait that long.lol)I have no dash board indicators. the dash board has been removed. Have no lights or gauges. Only the original headlite switch is still there. Blinkers, lights and brake lites all work.  

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/16/13 05:05 PM

Sounds like a good idea. will try it in the AM.(If I can wait that long.lol)I have no dash board indicators. the dash board has been removed. Have no lights or gauges. Only the original headlite switch is still there. Blinkers, lights and brake lites all work.  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/17/13 06:40 AM

Did get all ring terminals brushed brushed.Just measured the AC voltage from output post on alternator to case. got a 27 VAC reading. WOW.Much higher than the .02 I was looking for. I am sure it is an indicator for something.LOL.



well... at this point..  you have two choices..

you can replace the alternator..

or

you can rebuild the alternator..

the diodes are blown or shorted...

the issue is... replacement alternators are cheep... toss one on...

this is the rectifier bridge.  they are soldered in.. so not easy to change for the average person..

Ford1grectifierbridge

when you select a replacement.. please look thru the vents on the back.. and select one with NEW diodes. not remans all get new diodes...

i have a question.  

does this car have the shut off on the taillight panel to cut the battery power???

if the engine is forced to shut off by flipping the master switch off..   this removes the load from the charging system.. just like pulling a battery cable with the engine running..     the electrons rushing toward the battery have NO place to go when the battery is disconnected.. so the electrons build up and become high voltage.. this can happen in a split second..

alternator diodes as with all others are rated like this..    25 amp 100 V PIV.. peak inverse voltage..  if you get an alternator winding to exceed the 25 amps per winding.. you will damage the diode .. if you can get the alternator to create over 100 volts.. it will damage the diodeS

diodes/ rectifier bridges can be selected usually with  six.. 25 Amp 100 volt PIV diodes..

or six   50 amp 200 volt PIV diodes..  these cost a few bucks more each.. so they rarely get installed by rebuilders.. many that i have talked to.. deny they exist..

one other thing.. PLEASE REMOVE THE DIODE in the Field circuit..

if you looked at one of the diagrams that i have..  i seem to recall that the voltage regulator might actually ground the field winding when its not supplying power.. this reduces the magnetic field and prevents the rotating field from self energizing and creating a run away charging system..

if you have a diode... preventing the field winding from being grounded by the regulator.. you will have an issue that might create a smoke issue with other components.. as in letting the smoke out..

last thing and i think you have solved the high voltage reading from the stator connection...

do you have an aftermarket ignition system..  like an MSD box.   please be sure to ground the big ground wire to the engine block.. not just the battery.  with the rest of the system passing the voltage drop test  the ignition system has a HIGH VOLTAGE spark return path.   you don't want the spark return path being long getting back to the box.... i can explain it more if you want..  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/17/13 06:45 AM

oh.. this is the diagram...

Fordchargelitealtdrawing

look at the FLD circuit inside the voltage regulator..

note that its a double contact.. positive on one side.. ground on the other..

with the diode in the circuit..  its going to prevent the regulator from controlling the field circuit..  so you would have a runaway charging system..

REMOVE THE DIODE from the fld circuit..

when you pick up the replacement alternator.. with your issue of crazy high voltage on the stator winding.. replace the voltage regulator again... there is a chance that the coil the stator winding is attached to is damaged.. or if its an electronic regulator inside the case.. it might be damaged.. replace both ..

then rerun the 4 steps of the voltage drop test.. post results..

welcome to the world of being able to completely fix invisible electrical issues..

now.. for your daily driver and your wife's car..  run the voltage drop test..

you will find that all cars work so much better when you get the voltage drop down to within my readings.. especially the computer controlled cars..  

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Rohan-2
New User
Posts: 16
Joined: 07/13
Posted: 07/17/13 08:03 AM

Thanks Wayne. I wanted to let you know that I tried what 54packman said this AM(and thank you 54packman). I fired up the car and touched my test light to the I terminal on regulator. My test light flashed and the alternator started charging. But... it was charging 15-high 16 volts.  Tested a couple times and had to do this each time To make it charge. Will not charge if I dont touch the I terminal.Still think I should change both alt and reg ?
Many thanks again ..
Smirk  

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waynep712222
User
Posts: 223
Joined: 04/13
Posted: 07/17/13 10:16 AM

well.. hmm..

~~~~~~~~~~~~~~~~~~~~~~~~~~

first remove the diode from the FIELD circuit.. if you have not already done so...
with the diode installed the voltage regulator can only increase the field strength.. it cannot ground it to reduce it..  so the alternator will overcharge..

~~~~~~~~~~~~~~~~~~~~~~~~~~



does the A circuit at the regulator go on and off with the key???? if so.

lets see... do you have a 194 bulb in a socket??? an old side marker bulb and socket???

jump the A circuit thru the 194 bulb and socket to the I terminal...

see what happens then...

if the A circuit is NOT switched.. and i have gotten out my books but not had a chance to dig in yet..   you will need to find another switched positive.. without a resistor like would be in the coil positive circuit..

you still will probably have way TOO much AC voltage on the STATOR circuit..  

which should be HALF the DC OUTPUT Voltage ...

i guess i will have to go out to my 76 E250 or my 70 Ranchero and fire them up to measure the voltage on the stator wiring of a properly operating charging system..

as for replacing both.. that is what i would probably try...  unless you live really close to the parts store.. or will just try it for a few seconds..

when full fielding.. you are supposed to limit the voltage to NOT go very far over 15 volts.

well your factory wiring is interesting...

the yellow wire on the A circuit is not switched..  its hot all the time .. but you car was / is wired for an amp meter..

now.. there are slight differences depending if you have the conventional alternator with wire terminals on the back  or the larger amp version with a T connector on the side for the FLD and STA circuit..

~~~~~~~~~~~~~
there are multiple wires coming out of the alternator output wire splices..

looks like the black and orange wire from the back of the alternator goes to a splice and then continues to the yellow wire thru a fusible link and to the starter relay ...

from the splice it also stays yellow and thru a different fusible link and powers a bunch of stuff like the fuse for the hazard flasher.  the radio? and 2 connectors on the ignition switch.. also the rear window defroster if equipped.

from the splice yellow becomes black and orange powers the headlight switch and 2 fuses the dome light fuse and the horn and clock fuse..

from the splice yellow becomes yellow and light green and goes to the instrument cluster probably for the amp meter circuit..

from a second splice yellow becomes red and orange and goes to the instrument cluster.. probably for the amp meter circuit.  

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