How do I troubleshoot my rebuilt generator that is not generating on 48 DeSoto?

[marcapra]

Today, I called the guy who rebuilt my generator because it isn't charging.  He told me to do some electrical tests of the generator and regulator.  The shop manual has some techiniques, but they are hard to understand.  I recharged my battery with my Noco Genius charger.  With the engine running, I checked the battery voltage with my multi-tester and it read 6.3.  Then I tested the regulator BAT terminal to ground, and it also tested 6.3 volts.  Then I tested the A terminal of the generator to ground, and it tested 0.  I don't know if that is a real test though.  I also tested the regulator terminals to ground and there was continuity.  So I think the regulator is grounded.  So I need to read up on how to do further testing to find out where the trouble is.  The ammeter has never gone above 0.  I thought it could be a bad ammeter, but I checked the battery voltage after about 30 minutes of the engine running, and its voltage had dropped.  I need to do some more tests of the generator.  Does anyone have some tests they would recommend?  thanks, Marc.

Edited July 13 by marcapra (see edit history)

[Bloo]

26 minutes ago, marcapra said:

I checked the battery voltage with my multi-tester and it read 6.3.

Yep, that's a fully charged battery and the system is not charging (would be over 7 volts if it was working). You do need to have the engine running faster than idle for any valid testing of the charging voltage.

 

26 minutes ago, marcapra said:

Then I tested the A terminal of the generator to ground, and it tested 0.  I don't know if that is a real test though.

It doesn't tell you much that is useful. It does tell you the cutout has not pulled in, but that is expected. The generator has to try to charge to pull it in. That terminal would be connected to the battery if the cutout was pulled in. We can see from 6.3v that the system isn't charging, so yeah, normal.

 

Have you polarized the system? The "correct" method varies by make and model, and it does matter. Polarize it using whatever method your shop manual says, and see if it starts charging. If not, I might have some more ideas.

 

Edited July 13 by Bloo (see edit history)

[marcapra]

I told the electrician that I polarized the generator and he said why did you do that.  We always polarize generators in the shop before we give tham back to the customer.  He said my generator and regulator were bench tested hooked up together and it was producing voltage great.  

[marcapra]

I found a good YT video on how to troubleshoot a 6 volt tractor generator.  She shows four simple tests to do that would be similar, I assume, to my 48 DeSoto generator.  I like how she shows how you rule out the regulator by bypassing it, and then rule out, or rule in the generator itself as the culprit.  Since my generator was just rebuilt by a very reputable electric shop, I don't know what could be the problem with mine.  

 

The four steps of troubleshooting the charging system shown in the video are

1. See if the gauge is working while the engine is running.  

2. While the engine is running, remove the ground cable from the battery.  If the engine does not stall, the generator is working.  

3. On the regulator, put a jumper cable on the F terminal and the other end to the ground on the generator.  This bypasses the regulator so you can see if the generator is good.  Start the engine and you should see the ammeter go up.   

4.  Test the generator by removing the fan belt.  With the engine off, connect a jumper wire to the F terminal of the generator and ground the other end.  Then, connect a jumper wire to the neg post of the battery and touch the other end to the A terminal.  The generator pulley should spin if the generator is working.  

 

 

[Bloo]

I don't doubt any of it, but that is because she knows exactly what she is working on.

 

4 hours ago, marcapra said:

1. See if the gauge is working while the engine is running.  

Yep.

4 hours ago, marcapra said:

2. While the engine is running, remove the ground cable from the battery.  If the engine does not stall, the generator is working.  

That was never a recommended test (it's a little hard on things) but you will be fine on a 48 model. The contacts will rattle and the engine will miss if it's charging, but no harm done. If someone with a 3 brush generator does that, the generator's field coil burns out.

 

4 hours ago, marcapra said:

3. On the regulator, put a jumper cable on the F terminal and the other end to the ground on the generator.  This bypasses the regulator so you can see if the generator is good.  Start the engine and you should see the ammeter go up.  

Err.... Maybe. This is called "full fielding" the generator. It is a valid test. The trouble is, there is the "GM" system, and the "Ford" system... or depending who you ask, maybe the "Delco" System or the "Autolite" system, or "A circuit" and "B circuit". Confused? Me too. Delco has made both kinds and so has Autolite. Ford used one type for years and then changed when they went to 12 volts.

 

Mopar? I'm not sure. This is why you really should get info either from the factory shop manual or a MoToR or Chilton etc. that covers the the exact system you have in detail. If memory serves, it is like 6 volt Ford, but I am not sure enough of that to start jumpering things without looking in a book.

 

The difference between the 2 types is on one type you ground the field terminal to make it charge, and on the other type you send voltage to the field to make it charge. How to tell? Well if you have anything that shows the internal wiring of the generator, and the main wiring diagram might, check to see what the field is connected to. The field is the non-moving set of coils.

 

If one end of the field is grounded internally and the other end goes to the field post, then you send the field post 6 volts to charge.

 

If one end is connected to something hot internally, like the armature post or hot brush, and the other is connected to the field post, then you ground the field post to charge.

 

Important: If you just try both, be sure the field wire is disconnected from the regulator. The generator wont care if you try both, but the regulator sure could get damaged. The best way is to know which method works before you do it.

 

4 hours ago, marcapra said:

4.  Test the generator by removing the fan belt.  With the engine off, connect a jumper wire to the F terminal of the generator and ground the other end.  Then, connect a jumper wire to the neg post of the battery and touch the other end to the A terminal.  The generator pulley should spin if the generator is working.  

Well.. that is an old fashioned test called "motoring" can can give you a clue if the generator is working. It is subject to the same things I mentioned in #3. You need to have voltage across the field. Whether you would ground the field or feed it voltage depends on what the other end of it is connected to. I never do this one, not that there's anything wrong with it, but I usually know whats wrong before i get around to doing stuff like taking the fan belt off. I think you will too. The motoring test was mainly the sort of thing you did on the floor down at the junkyard to see if a used generator had a good chance of working.

 

The battery is hooked up positive ground, right? All 6V Mopars of the period were positive ground.

 

Edited July 13 by Bloo (see edit history)

[Oldtech]

If the generator passes the test then re-check wiring and try a different regulator, if one is available.  Or Bloo can suggest some regulator tests. 

[marcapra]

Yes, my car is 6 volt positive ground as all Mopar, and maybe Fords, were before 1956.   I will check my shop manual for tests, but it is not very user friendly and assumes you have 1940s type testing gear.  If anyone knows of a better video than the one above for 6 volt cars, please provide a link to it.  Thanks, Marc.

[marcapra]

I'm not going to try the no. 2 test.  The shop manual says "Caution:  whenever any part of the generator system is disconnected, or battery cables are removed while the engine is running, there is a danger of injuring generator."  I think I will only do tests that the electric shop guy says I should do to avoid ruining my warranty.  

[Frank DuVal]

18 hours ago, marcapra said:

She shows four simple tests to do that would be similar, I assume, to my 48 DeSoto generator.  

 

This is the place to NOT ASSUME! Magic smoke can leave the system if you do the wrong tests.🤬

 

There are A circuit and B circuit generator systems. As Bloo says, the major manufacturers made both types, so DO NOT GO BY brand! You have to know from the shop manual, Chiltons, Motors, etc.  or ask the rebuilder what tests he suggests. Which terminal of the battery is "grounded" i.e. connected to chassis, is not how to tell A circuit from B circuit. Both can be both.

Edited July 14 by Frank DuVal (see edit history)

[marcapra]

After thinking about it, I thought I don't have to do any complicated tests on the generator or the regulator.  They work fine like my electric shop man said.  It has to be something simple, but major.  It probably has something to do with the wiring.  So I asked myself how could I change the wiring just to see.  Well, I wired the ground brown wire to the A terminal like the wiring diagram said.  Others have said I should mount that brown wire to the generator ground screw.  So I sanded the black paint off the ground screw hole and put the brown wire under the ground screw.  Immediately, the battery voltage started going up!  Then I checked the ammeter and it was going up to 30 amps when I gunned the accelerator.  Problem solved!  

Edited July 14 by marcapra (see edit history)

[Bloo]

33 minutes ago, marcapra said:

Others have said I should mount that brown wire to the generator ground screw.  So I sanded the black paint off the ground screw hole and put the brown wire under the ground screw.

Doesn't the other end of that brown wire go to the starter relay? If so the problem is not yet solved.

 

If the other end of the brown wire goes to ground, then maybe it is solved. That's not how i remember it though. There seem to be a multitude of threads about this same car, often about electrical things, and apparently only one has the wiring diagram in it?

 

What I would do (assuming the brown wire is not grounded the other end):

 

1) Add a ground wire from the generator to the block.

2) Find both ends of the brown wire, disconnect them, check for continuity through the wire, check that there is NO continuity to ground, and then reconnect the brown wire according to Chrysler's wiring diagram.

 

And then:

 

3) Ask yourself how things are grounded. The engine must be grounded, but so must the body since it has electrical things grounded to it. Also the frame most likely needs to be grounded for the same reason. Current flows in a circle, and what we call "ground" is just the last part of the circle.

 

If your battery "ground" (+) strap goes to the body or frame, then an equally large and capable strap (or cable) needs to go from whichever thing they used (body or frame) to the engine.

 

If your battery "ground" (+) strap goes to the engine (probably better), then the body must be grounded with a wire or strap or SOMETHING. How did the factory do it? In the 60s, Chrysler ran a small ground strap from the back of the engine block to the firewall. I'm not sure what they were doing in 1948. It does not need to be a huge strap or wire because it does not carry starter current, but it must be there, because many things ground to the body, including the voltage regulator. The frame must also be grounded if anything is grounding through the frame.

 

Some cars have a redundant ground wire from the generator case to a bolt under the voltage regulator. This makes absolutely sure the generator and the regulator have the same ground. If the car didn't have it, then technically you don't need it, but that was only because they grounded everything (body, engine, and possibly frame) together in some other way.

 

I'd still add a ground from the generator case to the block no matter what. You can probably find a way to hide it if you don't want it to show.

 

Edited July 14 by Bloo (see edit history)

[marcapra]

The other end of the brown wire goes to the starter solenoid.  I've been told it's a ground.  I do know that if I try to hook up a remoter start switch from the neg. post of the battery to that terminal the wire gets red hot real fast.  ( you see the specialist who rebuilt my solenoid switched terminals on me without telling me!).  So now the brown wire goes to the upper outside terminal of the  solenoid.  I'm pretty sure it's a ground.  My battery ground cable goes to the generator mounting bracket, which is bolted to the block.  I did buy a ground cable with two eyelets so I could ground the body to the block, but I haven't installed it yet.  I know other DeSoto owners like Nutaitis who owns a 48 and a 41 say that the brown wire goes to the ground screw on his cars.  

Edited July 14 by marcapra (see edit history)

[Bloo]

It's the ground for the starter relay. If you connect it to the armature terminal, then you cannot grind the starter when the generator is charging. If you connect it to ground then you can grind the starter when the generator is charging. Why? Because when the generator is charging, the armature terminal is a 7+ volts so the starter relay has no ground. When the generator is not charging, there is a path to ground through the armature and brushes, so the starter relay is grounded, or at least grounded well enough to work. Buick used the same trick on their autostart system from roughly 1940 until they stopped using the system in 1960. It's a safety device to keep you from accidentally grinding the starter. it has nothing, and I do mean absolutely nothing to do with whether the system can charge or not.

 

If connecting that brown wire to the generator case is what made things work, then something wasn't grounded, period.

 

If it should turn out that the system works fine now, brown wire or not, then probably you polarized the system with or without knowing it. I have never heard of someone polarizing a generator on the bench and then telling you you don't have to. Maybe he knows something I don't, but back in the day polarizing the generator before starting was job one before starting the engine after doing any kind of charging system work. Any old service manual will back this up. The method of polarization needs to be match the system, or it might not get polarized, or in some cases the regulator can be damaged. 

 

57 minutes ago, marcapra said:

 I did buy a ground cable with two eyelets so I could ground the body to the block, but I haven't installed it yet.

There is a very high probability this is the original problem. Did Chrysler have one? If so, you need it. If they didn't, investigate how they did ground the body.

 

57 minutes ago, marcapra said:

 ( you see the specialist who rebuilt my solenoid switched terminals on me without telling me!).  So now the brown wire goes to the upper outside terminal of the  solenoid.  I'm pretty sure it's a ground.

To find out, disconnect the brown wire completely. If that terminal is the ground for the starter relay, and the correct one to be connected to the brown wire, the starter will not crank.

 

EDIT: That starter solenoid is confusing. 2 relays inside maybe? I see a separate post for the Sisson choke. They probably don't want that on unless the engine is running and the generator is charging. I'm not sure exactly how they accomplished it, but I doubt it changes anything about the charging.

 

Edited July 14 by Bloo (see edit history)

[marcapra]

I did connect the brown wire to the A, but my generator would not charge.  Are you saying I should ground the generator case to the block to ground the generator?  Where would I connect the ground cable on the generator case?  And isn't it already grounded to the block through the generator mounting brackets?  There is an excellent thread about this subject from a awhile back.  Carl N. says some interesting things and shows a pic from his 48 DeSoto with the brown wire connected to the ground screw.  

 

Edited July 14 by marcapra (see edit history)

[Bloo]

@Oldtech explained what that brown wire is in the second post of the linked thread. You can indeed hook that wire to the ground screw like CarlN-NDC's car if you want. Maybe it's factory. It makes no difference to the charging system. None.

 

2 hours ago, marcapra said:

 And isn't it already grounded to the block through the generator mounting brackets?

It should be. Why isn't it? Paint? If it were grounded through the brackets, it wouldn't need to find a substitute ground through some random brown wire and starter relay windings in order to work. Fix your grounds and all will probably be well.

 

Note: if the generator/block and the regulator/body do not have the same ground the voltage regulation cannot work properly. Is this car supposed to have the block to body strap you mentioned buying? If so, put it on.

 

 

[Frank DuVal]

10 hours ago, Bloo said:

If connecting that brown wire to the generator case is what made things work, then something wasn't grounded, period.

I disagree! That brown wire IS grounded, holding the A terminal of the generator at zero volts while it is bootstrapping up from residual magnetism. Since the A terminal being grounded by the brown wire, no charging will happen. I suspect the brown wire is mis-wired on the solenoid end, or chaffed wire in the middle of the run.

[Bloo]

i did suggest testing that... However it was clear in the other thread that having the brown wire disconnected causes the starter not to crank, so the brown wire is likely connected where it is supposed to be at the other end, and the generator is finding a ground through the starter relay or solenoid.

 

Edited July 14 by Bloo (see edit history)

[Frank DuVal]

Missed that. Hmm , mystery continues. Then has to be miswired solenoid, or wrong solenoid causing miswire for the brown wire to be grounding the A terminal. A quick ohmmeter reading would have answered some questions as you say. 😉

[Bloo]

I don't think it's grounding the A terminal, but I can't be sure. That is an interesting thought.

 

Edited July 14 by Bloo (see edit history)

[marcapra]

I should say that my electric shop did send my solenoid out to Maine to be rebuilt by a specialist, since Richer electric said they didn't have the parts.  The specialist did make some changes to my solenoid, such as reversing the polarity between the two top terminals.  I don't know what else he did, but he may have disabled the brown wire terminal from working the way it should.  I just tested my generator case to block with my multi-tester and I do have continuity, so I am not sure what putting a ground strap on the generator would do?

[JACK M]

Block to chassis, chassis to body. These all have to be grounded together one way or another.

And all these grounds should be hooked up before any electrical testing on any part of the car.

A wise old guy told me once that " most all electrical problems are groundless".

[Frank DuVal]

On 7/14/2024 at 1:08 PM, Bloo said:

I don't think it's grounding the A terminal, but I can't be sure.

Going by what we do know, it must be. What do we know? If the brown wire is on the A terminal then the A terminal never rises above zero volts with the engine running. When the brown wire was removed, and no other changes, the A terminal bootstrapped up (due to residual magnetism) to a voltage high enough to pull in the cutout in the regulator. So, the brown wire must be grounding the A terminal. QED. and a 😉

[Bloo]

6 hours ago, Frank DuVal said:

Going by what we do know, it must be. What do we know? If the brown wire is on the A terminal then the A terminal never rises above zero volts with the engine running. When the brown wire was removed, and no other changes, the A terminal bootstrapped up (due to residual magnetism) to a voltage high enough to pull in the cutout in the regulator. So, the brown wire must be grounding the A terminal. QED. and a 😉

That much sounds reasonable, but one little nitpick. The brown wire wasn't just removed, it was removed and and connected to the generator case. We also know that disconnecting the brown wire from the generator case causes the starter not to crank. Any idea how that could happen if the brown wire is simply grounded?

 

Edited July 16 by Bloo (see edit history)

[marcapra]

The starter always cranked, but it was always connected to the A terminal, and then to the ground.   

[60FlatTop]

You really need to take all your known data and make a ladder diagram on the system. Each line will create a readable sentence of the operation.

Then add devices and trace the wires filling in the complete circuit. It will read like a sequence of operation when completed.

 

I have used ladder diagrams with up to 200 lines on electrical equipment and 2,000 lines of ladder logic. It is easy when you get into it.

[Frank DuVal]

On 7/16/2024 at 6:15 AM, Bloo said:

Any idea how that could happen if the brown wire is simply grounded?

Ah, the English language again. 

 

I said Grounding  not grounded. Something on the brown wire has a low enough resistance to chassis to kill the bootstrapping effect of the residual magnetism. Like the coil of a solenoid say, or some other load. 😉

 

I think we agree on what is going on. But not why it is going on now, as originally wired/equipment the generator worked with the brown wire on the A terminal. According to the wiring diagram. And from miles away, we will never know what wiring has been changed in the circuit.👍

[marcapra]

All I know is the rebuilder changed the top left terminal of the solenoid to the top right, and the top right to the top left.  Why I don't know.  I had to discover that for myself when I tried to hook up the hot wire to the top right terminal and got a red hot short!  All I know is that the starter and generator are working now, so I will let sleeping dogs lie.