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After a moderate time in storage, the 1970 Cadillac started well on her own battery. She was driven home, about ten miles - then it would not start as a result of a discharged battery. After a jump-start, a quick check showed that the wire between the alternator and the battery was right at 12-volts, rather than the expected 14 +/- volts which would have been typical. After checking wires and contacts, I removed the alternator and took it to the brand new Autozone store where they checked it and said that it was putting out over 14 volts.

 

Since I plan to tour cross-country with this old girl (the car), I bought a new Voltage Regulator, and a new Alternator (which they also checked and was showing over 14 volts).

Back home, I re-installed the old but good alternator and the new regulator. The same condition - only 12 volts, so

 

then I swapped out for the new alternator - same lack of results !!

 

What am I missing? In the old days we had to polarize by jumping across terminals on the regulator, but I didn't think this was a factor with an alternator.

 

I'm at a loss, and don't have much more hair to pull out.

 

What am I doing wrong?

 

What do I need to do to get the system charging?

 

I appreciate any help and advice for you all - notably the best bunch on the planet.

 

Thanks in advance for your thoughts,

 

Marty

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Edited by Marty Roth (see edit history)
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Electrical problems often vex me, too, but I had a similar issue with my wife's '66 Mustang. It turned out that the battery was simply going bad. It usually had enough juice to start the car, but even when it was running, voltage was low. I know that the battery on my '29 Cadillac is also the voltage regulator (not current) and assumed that was also the case with the alternator-equipped Mustang. The battery might just be tired.

 

There are surely guys with real knowledge, not just an anecdote and a wish like me, but that's an easy thing to check/replace.

 

Hope this helps!

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I agree with Matt. I just ran into the same situation with my Jeep Patriot while my wife had it out-of-state visiting her mother, of course. If the vehicle sat for any length of time, only a call to AAA would get it started. Upon her return home, I did the cheapest and easiest thing first, and replace the battery with a known good one. The engine started every time since. Wife keeps asking when I'm going to buy a new battery and I just tell her that I'm still testing it.

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Just prior to this event, I had occasion to check the charging system, and it showed 14 volts. The battery seems to hold a charge just fine and will start and restart, and restart the car over and over.

 

The issue is the , even when running, the system is at a flat 12 volts - the alternator which puts out 14 volts on test equipment, only is at 12 volts when on the car, and the original regulator, and both replacements make no difference. 

 

Is there an "Exciter" wire going somewhere to some terminal which may be broken? The alternator light on the dash stays "ON" now where it went off when the charging system was working.

 

Where is the fuse which Helfen referenced?

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Larry W. also suggested that as Matt said, the battery is just old, and that affected his car's starting. Replacing his battery allowed his car to start.

 

My car's problem is NOT affecting the battery's ability to hold a charge, nor is it affecting the ability to start.

 

The battery hold a a good charge, and the car starts just fine.

.

My problem is that the charging system is not going above 12 volts where it should be at 14+/- Volts.

 

Thanks for your thoughts.

Edited by Marty Roth (see edit history)
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 Marty, Before GM went to the IC alternator there was a inline fuse ( looks like a 60's 70's radio type buss type fuse holder ) usually on most GM cars that in Pontiac's and some Oldsmobiles ( could be others, but I know those types and years well )  in the harness coming from the alternator. Those fuses are the buss type and can depending on the type of accessories go from 35 amps to in the case of A/C cars to 65 Amps. I have seen some over 100 amps. If you cant find this fuse at or near the back end of the alternator I'm afraid you'll need a service manual so that you will know where to look so you know . In the diagram C49er you can see a fusible link, frankly I didn't or hadn't seen any such link in those years of GM cars, but right where the link is pictured in the picture is where my radio style connector buss 65amp fuse is located. If your car does have a fusible link it is possible that it is taped up with the harness close by. But finding it is why you need the manual.  

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if that had blown he would have no charging volts at all

 

Ted, according to Marty, he has no charging volts. Charging volts would be about 14.5 volts He is picking up battery voltage (12V) which goes from the battery to the starter to the alternator harness. He needs to check voltage from the alternator harness to the regulator. In the case of your schematic that would be 12 volts to the regulator # 2 terminal. 

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Battery cables can fool you.  They can look clean, but have enough subtle corrosion to prevent passage of current. Does the car have a large cable AND a smaller one going to the positive terminal?  If so the trouble may be that the heavy cable is making contact to crank the engine, but the smaller one through which I believe the alternator current would flow isn't in good contact.  If they come apart separate them and clean them VERY thoroughly.  If they are in one piece, consider replacing it, unless the smaller cable can be isolated and its continuity can be verified. To check afterwards look for the alternator light to go out when you start up, and voltage to rise to about 14.5 volts on the dash.  Good luck.  I remember the time you had with a master cylinder.. 

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Check the volt reading right off the output stud on the alternator.. should be 14.5 volts . If it's correct there and not at the battery..certainly a wiring issue. An open or shorted wire.

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Thanks to all (Matt Harwood, Helfen, Dave Henderson, c49er, Larry W, Ted Sweet),

 

I found a lightweight wire which had an internal break, and was making ground instead of going to the  "BAT" side of the alternator. Too bad I didn't catch this before replacing the original alternator and regulator. This car has the main "Positive" battery cable going straight to the starter solenoid, and another from the battery "+"  directly to the alternator where the lighter wire was also to have made its connection. Not having this connection, and the wire being grounded instead seems to have been the issue. 

 

Now we have 14.8 Volts at the alternator and battery terminals when the engine is at idle. The battery voltage drops a bit when all 4 high beam headlights are on and the automatic temp-control A/C's blower is on maximum".

 

Thank you all for the comments and suggestions. You are examples of the wealth of knowledge and technical information retained by our "Old car" community, but the best part is how quickly you were available to share your thoughts. That is part of what make this hobby - and the AACA FORUM - such an important part of our lives.

 

With sincere appreciation,

 

Marty 

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Edited by Marty Roth (see edit history)
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 Marty, I have a request if it's not too much trouble. Can you take a picture where this wire is located and if you have any bits or pieces of the harness and show those pieces too.

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 Marty, I have a request if it's not too much trouble. Can you take a picture where this wire is located and if you have any bits or pieces of the harness and show those pieces too.

I'll be happy to get the photo as soon as I can get back to the Caddy which is now back in storage while I catch up on other maintenance.

 

The wire in reference is just a single wire which runs from the bigger stud on the back of the alternator where the heavier wire also goes straight to the Battery's "+" terminal. The small repaired wire runs along the passenger side of the engine and through the firewall. I've not yet had a chance to trace it to see if it goes to the fuse block or directly to the ignition, but if I had to hazard a guess, I'd say that this wire served to "excite" the alternator.

 

Thanks again for your help and advice. I'll see about getting a picture ASAP, but don't think it will add anything.

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I'll be happy to get the photo as soon as I can get back to the Caddy which is now back in storage while I catch up on other maintenance.

 

The wire in reference is just a single wire which runs from the bigger stud on the back of the alternator where the heavier wire also goes straight to the Battery's "+" terminal. The small repaired wire runs along the passenger side of the engine and through the firewall. I've not yet had a chance to trace it to see if it goes to the fuse block or directly to the ignition, but if I had to hazard a guess, I'd say that this wire served to "excite" the alternator.

 

Thanks again for your help and advice. I'll see about getting a picture ASAP, but don't think it will add anything.

 Marty, It's more of a learning experience  for me. I am curious about how different GM's divisions can be from one another. You know the old saying "a picture is worth a thousand words". Thanks in advance!

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  • 4 years later...

I am having the same problem on my Pontiac; New alternator, new battery, new starter, new regulator cannot get over 12.7, from the replies on this site or chat or whatever- Sounds like I need to do some continuity checks and wire tracing... when it’s warmer currently its 1 outside- 

 

Want to thank everyone for posting wiring diagrams. Btw this post is 4 years old I don’t exactly expect a response to my previous paragraph but if I get one, thanks. 

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Yes, probably wiring. I would check the voltage from the BAT terminal on the back of your alternator to the case, and compare to the voltage at the battery. They should be real close, as they are wired together (if nothing is broken)

 

Fusibile links (or fuses if you find one as described in the replies above) are suspect if the 2 voltages aren't close to the same.

 

Is the GEN light on? It should be if the system isn't charging. If it is not on, thats a clue.

 

Welcome to the forum! There are plenty of helpful people around here. We can help you sort it out.

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As far as I can tell with certainty G M vehicles of that era does not use external regulator. It is all built in the alternator. If the car has no volt meter on dash, it has an idiot light. The alternator  is usually a 15 S1, anything from 65 to 90 amps depends on energy use, all the bells and whistles. Turn the key on and the idiot comes on or  the voltmeter needle leans to the left. Start the engine and the idiot light goes away. The terminal on the alternator is a block. Pull the block out, turn the  key on and check the small wire that goes to the "I" That is the idiot light wire. Check the wire that says "f" That is the field wire and the fat wire, usually 12 gauge, is the battery wire. They should all have juice. Another check. remove all wire from the alternator and put a jumper wire from battery to the battery terminal on the  on the alternator and a jumper from the battery and to the "f" terminal. Start the car and  rev about 7 to 8 hundred RPM. A good alternator will charge about 14.5 volts - + . If you hook up an amp meter  and rev at about 3000 RPM the output should read about 3/4 of the rated output of the alternator.

A problem could be a worn out battery.  If it is side mount terminal battery remove the terminals and clean. also sometimes the battery terminals develop a film of clear plastic like insulation which must be scraped,  including wire  terminals. A common problem with Delco Side mount  batteries . Try removing the onboard battery cables and use a jumper battery  using the onboard battery wires .CHECK AND CLEAN THE GROUNG WIRE . An interesting check is use a jumper and ground the alternator to a good body ground . If it is a ground problem the voltage will jump up. I would like to hear from you how you solved the problem.    

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That was about the time some car lines got a 10SI (internal regulator) and think it was about '72 before all of the 10DNs (external regulator) were replaced. If you can be specific about the year, engine,  make, and model I can tell you which alternator was supplied. Near 50 years on 10DNs were often replaced by 10SIs but normal car lines still had less than 100A, base models often had a 37A.

 

Delco alternators usually had a contact on the back near the bottom where you could stick a screwdriver while running and it would go to max output.

 

Upgrades are popular and common, think the max is about 140A

 

Back in the day I used to reverse the diodes in a 10DN & use in Jags with lotsa halogen lights (had to be imported then).

 

BTW you realize this thread is from 2015 ?

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K... turned everything on; lights, heater/fan, radio.... put the meter on it read back forth between 12.7 to 12.9.... talk of the alternator its a 60 amp unit from rockauto, has a needle guage in dash no light.

 

volt regulator is like the alternator 3 wires- I’m in Alaska its 15 snowing (that will be the extent of my whine lol) 

 

started right up no jump but I brought the battery in charged it up cleaned the heck out of the terminally and connectors- 

 

wonder if a guy can run a 10 gauge from that alternator to the positive terminal? 
 

an old guy said if the battery is good the alternator won’t come up? I dunno thought it was always 13 or + so running... 

 

 

 

 

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1966 389 Catalina BOAT lol my baby lol

 

K... turned everything on; lights, heater/fan, radio.... put the meter on it read back forth between 12.7 to 12.9.... talk of the alternator its a 60 amp unit from rockauto, has a needle guage in dash no light.

 

volt regulator is like the alternator 3 wires- I’m in Alaska its 15 snowing (that will be the extent of my whine lol) 

 

started right up no jump but I brought the battery in charged it up cleaned the heck out of the terminally and connectors- 

 

wonder if a guy can run a 10 gauge from that alternator to the positive terminal? 
 

an old guy said if the battery is good the alternator won’t come up? I dunno thought it was always 13 or + so running... 

 

 

 

 

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Have you checked the voltage at the alternator AND the battery? Are they close to the same? Try it with the engine not running, or running. Either way, the results ought to tell us something.

 

Figure out whether that circuit is broken before you go about replacing it. As referenced by the earlier Cadillac posts, there is probably a fuse or fuselink, and it's probably bad. I'm betting on a fuselink.

 

If that circuit proves to be good (I doubt it), the next step would be to "full field" the alternator to see if THAT makes it charge.

 

Yes 12.7-12.9 means it isn't charging. It probably charged at about 14.2V when new, however GM (apparently) jacked up the charging rate around 1976(?) to better match the chemistry of their newly introduced "Freedom Battery". 14.7 or so became the norm for GM, and the aftermarket quickly followed suit with their voltage regulators. Today GM cars in the wild (with alternators) are usually found to be charging at the higher rate, even when they are much older than 1976, all the way back to the first Delcotron alternators.

 

These numbers are not absolute, although they are pretty close at room temperature. Regulators are usually temperature compensated, and may jack the voltage up a tenth of a volt or two in the cold.

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Fuse in the harness  usually  affect the ignition. The engine will crank but there will be no ignition.  fuse in the  the harness?  Look for an unusually "fat"  lumpy wire about 2 inches long compared to the rest of the wire in the harness. To repair open the fat part and replace with an inline fuse.

Newer alternators has built in regulators. There are new versions with only one wire.. A short check is hook a jumper from the battery direct to the B terminal and use a jumper directly from the F terminal to the battery and run the engine at about 1000 rpm. with engine running turn on all bells and whistle and the engine will slow down.. GOOD GROUND IS A MAJOR PROBLEM. ENGINE TO FRAMEAND FRAME TO BATTERY.  Infrequent driving or  not driving enough to allow the battery to charge is a major problem especially with generators.   A WARM GROUND WIRE IS AN INDICATION OF POOR GROUND.

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You may put 4zero wire to the "BAT" terminal. It will make no difference. Just use a 12 gauge directly from the battery to the "BAT " terminal" Use a short jumper and attach one end to the battery and chuck the other end in the "F" terminal. That is to excite the field. (bypassing the key) That's all. Done. With engine running the charge should be 14.5 more or less. If the charge is above that , higher than 15 the battery is dead   If no charge look for poor ground . Leaving the jumper perminantly   from battery to "b" terminal will not cause any harm  There is a diode behind the "BAT" terminal that prevents the flow back . Look at the back of the alternator, just below the bearing, there is an elongated slot. Push a cotter pin in hard, that will ground the field brush. The voltage will go up to 18 volts. DO NOT HOLD FOR LONG. That is how to test internal problems in alternators with built in regulators.   Do the test with engine running of course.

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Just a gentle reminder in addition to all the excellent notes already posted-

 

When cleaning the ground connection, be sure to not only clean both ends of the wire, but also the surface to which they ground,

remembering to remove painted surfaces from the restoration.

 

You likely know this already, but sometimes a reminder triggers the "Oh-wow - That's what I did" moment-

ask me how I know...

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Ok... thanks to everyone tomorrow I will be a continuity checking guy- I want to check fuse-able links are shot. I would like everything to be square anyhow.  


reading all the importance of steps and ground etc... heres a btw: 

 

the ground for the voltage regulator (I assume) would be where its attached to the firewall, the other day when I put the new unit on; in the cold I lost 3 of the screws.... I figured one would be enough(?) but if that is indeed how its grounded maybe I should quit halfa*** things lol...  Or maybe that’s not how it’s grounded I gotta do it right though. 

 

ALL OF EVERYONE’s responses are much appreciated- This car being older than me by 11 years- my hat is off to this forum and all the members. I will be letting everyone know-

 

I start the car once a week let it run half hour. 

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13 hours ago, trini said:

As far as I can tell with certainty G M vehicles of that era does not use external regulator.

 

I've never seen a stock 66 GM product that DID NOT have an external regulator! 😲

 

Those internal regulator Delcotrons were a 70's design. 😉

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Bloo, You are right, but the car in question is a 1970 Cadillac.  If it is a  change over period then it might still have the outside regulator.

The easiest thing to do is to install one with internal regulator and leave the old regulator in place just for show. The "BAT" wire on the regulator could connect on the "BAT" terminal on the alternator and the field  wire could be attached to the "F" terminal on the alternator. Save yourself a lot of headache today and for the future. The "I" terminal is probably connected to the "BAT" terminal somewhere and is controlled by the ignition key. When the key is turned "ON" the dash gauge shows battery voltage.  THIS IS JUST MY THOUGHT. Old style housing is smooth outside and the new style has lots of ridges on the outside. I donot have my camera to show a picture of the difference. By the way I would just like to mention to check  if the new style alternator is charging touch a screwdriver blade on the bearing button with the engine running . There will bea strong magnetic pull.

CHEERS.    

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