Marty Roth

NOT CHARGING - 1970 CADILLAC

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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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Guest

Check the fuse in the harness near the alternator.

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Matt - The battery checks out fine

 

Helfen - I'll look again in the daylight, but did not recall any fuses near the alternator

 

Thanks to you both for the quick response

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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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Does the ALT or GEN light light up with just the key on?

It needs to work for the alternator to operate.

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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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Bob, thanks for the response.

 

The alternator light on the dash comes on when the key is on,

and also stays on when the car is running, both at idle, and at higher RPM.

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Looks like maybe a fuseable link wire to the regulator?

A couple GM wiring reference pictures...

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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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 That's great news! Good luck with your cross country trip!

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Glad you got it solved, Marty. There's nothing more satisfying than finding a problem and getting it fixed. Enjoy the road trip!

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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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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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