Alternator Overcharging
Pro
Joined: May 2005
Posts: 515
Likes: 66
From: Grosse Pte. Mich.
Need help in figuring this out. My alt. gauge hits the red and dummy light goes on but not all the time. Last year I replace the internal regulator and thougt it was fixed. Last week it happened again. Don't know if I should replace the alternator or if its in the wiring/connection. Has anyone had this problem?
Assumed it was the internal regulator so I replaced the alternator.
It has been rock solid ever since. (over a year now)
Safety Car
Joined: Dec 2004
Posts: 4,876
Likes: 1
From: Jersey Shore Exit 98
its the regulator not the alternator
Thread Starter
Intermediate
Joined: Mar 2007
Posts: 45
Likes: 0
At this point with everyones help, my next step will be to check all connections I have, replace the internal regulator again and I will report my findings and readings after that. Does anyone know how do I know if the alternator is bad vs. the regulator? Should I just replace the alternator and not spend the $$ on the regulator?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
In addition to the internal regulator, there are 2 sets of diodes inside. If the rectifier has a bad diode, it could also cause your problem- and they don't always check bad. Sometimes it's a thermal thing. and then while you've got the alternator apart, check the stator and rotor, diode trio, and the rectifier. All individually.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
At this point with everyones help, my next step will be to check all connections I have, replace the internal regulator again and I will report my findings and readings after that. Does anyone know how do I know if the alternator is bad vs. the regulator? Should I just replace the alternator and not spend the $$ on the regulator?
A new one at Kragen/Autozone is not much coin. Check your connections, change the whole thing out, and see how you do. There ain't much else to the charging system. 
I have had alternators that tested good, but had a bad diode. It makes electronic gauges go nuts.
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Thread Starter
Intermediate
Joined: Mar 2007
Posts: 45
Likes: 0
Well all....I just replaced the diode trio and the regulator. It appears my gauge is now reading a little bit more below the red. I would have to guess that the needle is showing close to 15 - 16. It does seem better. I guess I will be convinced after I take her out for some drives and see if the light comes on. I thank all of you for your help and I will update as I see changes or no changes after a while. Happy Easter!!
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Well all....I just replaced the diode trio and the regulator. It appears my gauge is now reading a little bit more below the red. I would have to guess that the needle is showing close to 15 - 16. It does seem better. I guess I will be convinced after I take her out for some drives and see if the light comes on. I thank all of you for your help and I will update as I see changes or no changes after a while. Happy Easter!!
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
Get a voltmeter, check the big red wire on the back of the alternator, engine running (output). If that is high, check the small sensor wire (the one on the plug that is hot with key off). With the engine running, see if the sensor voltage is normal ~13.5 volts. If the output is high on the output and the sensor wire normal, you've got corrosion/partially broken wire/etc or something causing a voltage drop in the system.
Gary
Gary
Last edited by Garys 68; Apr 7, 2007 at 09:22 AM. Reason: bad spelling
Thread Starter
Intermediate
Joined: Mar 2007
Posts: 45
Likes: 0
I just checked the "big" red wire with car running. My voltmeter red 14.6ish. I checked the red wire on the plug..is this the sensor wire? Did not get a clear reading (This was the connection from the regulator. Sorry for being so dumb. I did look closer at the guage and measure the reading. The markings are so close to eachother. It read a little over 15...like 15.2 or 15.3. So at this point not sure if I check the sensor wire completely.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
The sensor wire should show 12.5 volts with the ignition off. The excitation wire will show no voltage with key off.
If it's high at the alternator outlet (which it seems to) and low or inconsistant on the sensor, try running a short jumper wire between the outlet and the sensor wire. This eliminates the circuit in the car and should bring voltage back to normal, and effectively turns it into a 1 wire alternator.
But note if you leave it this way, it may result in slightly lower voltage if you have a lot of electrical accessories.
If it's high at the alternator outlet (which it seems to) and low or inconsistant on the sensor, try running a short jumper wire between the outlet and the sensor wire. This eliminates the circuit in the car and should bring voltage back to normal, and effectively turns it into a 1 wire alternator.
But note if you leave it this way, it may result in slightly lower voltage if you have a lot of electrical accessories.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
A 4 wire alternator has:
1) output, big red wire. Supplies voltage to the horn relay where it's distributed to battery, ignition accessories, etc
2) ground wire, black, grounds it
3) excitation wire, in the 2 prong plug, this is wired to the keyed ignition, it should have 12v only when key is in run position, even when engine is not turning. It tells the alternator when it should be on.
4) Sensor wire, in the 2 prong plug. This should show 12v all the time. It's wired into the harness and tells the alternator how much voltage it should be putting out.
If there's some corrosion or partially broken sensor wire, the voltage at the alternator sensor plug may read low. Then the alternator increases voltage because it thinks it's not putting out enough.
If you run a jumper between the output and sensor, it will simply sense the voltage at the alternator output terminal. This makes it similar to a 1 wire alternator, and it will probabl function fine.
1) output, big red wire. Supplies voltage to the horn relay where it's distributed to battery, ignition accessories, etc
2) ground wire, black, grounds it
3) excitation wire, in the 2 prong plug, this is wired to the keyed ignition, it should have 12v only when key is in run position, even when engine is not turning. It tells the alternator when it should be on.
4) Sensor wire, in the 2 prong plug. This should show 12v all the time. It's wired into the harness and tells the alternator how much voltage it should be putting out.
If there's some corrosion or partially broken sensor wire, the voltage at the alternator sensor plug may read low. Then the alternator increases voltage because it thinks it's not putting out enough.
If you run a jumper between the output and sensor, it will simply sense the voltage at the alternator output terminal. This makes it similar to a 1 wire alternator, and it will probabl function fine.
Thread Starter
Intermediate
Joined: Mar 2007
Posts: 45
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Ok Garys68....this is what I found. The output wire(big red wire)is reading 12.47. On the 2 prong plug, the excitation wire(white wire) reads 11.67 when key is on, the Sensor wire(red wire-hot all the time) reads 12.47. I think I understand the excitation wire reading 11.67 'cause of the drain of the fan on when key is on...right? If so, appears all is ok & if true, does this mean my gauge may be bad?
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
If these were the reading while the engine was running, yep it's a bad gauge.
And the excitation wire should read 0v with key off.
And the excitation wire should read 0v with key off.
Ok Garys68....this is what I found. The output wire(big red wire)is reading 12.47. On the 2 prong plug, the excitation wire(white wire) reads 11.67 when key is on, the Sensor wire(red wire-hot all the time) reads 12.47. I think I understand the excitation wire reading 11.67 'cause of the drain of the fan on when key is on...right? If so, appears all is ok & if true, does this mean my gauge may be bad?