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GaryP5

Battery Gage Fluctuates

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My 49 Pontiac starts fine and the battery gage moves to center. However, each time I step on the accelerator pedal the needle pegs to the right. When I come to a stop or idle it returns back to center nice and steady. 6v battery is fine and does not seem to be discharging. I've checked my belt tension, wires and grounds, changed and re-polarized the voltage reg to no avail. Any help fixing this would be GREATLY appreciated.

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I've already tried swapping to another used regulator and then to a brand new one with the same exact results, no change. I've also made sure that the regulator is polarized and grounded.

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Good chance that the voltage regulator coil points (not the cut out coil, or current coil, if so equiped) are stuck or welded together. I am not sure what you mean by "polarizing" a regulator. What are you doing?

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According to my manual (and the data sheet included with the regulator) I'm supposed to connect a jumper between the batt and gen tabs on the voltage regulator to ensure it polarizes to the generator (6 volt negative ground system). Everything with the car is fine, no other problems but the battery gage fluctuations. I'm at a loss.

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Did this problem happen out of the blue or did it happen after working on the system. Do not worry about polarizing... this is something that is done to a generator that has sat for 80 years not being used.

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I did work on the system this winter removing the generator and most of the other accessories to paint the block. The entire charging system including the wiring is fairly simple with a generator, regulator, gage, and battery connected by a few wires. I took many pictures and am pretty certain I put it all back together properly but must have missed something or made an error.

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Ahh, I think that there is something wrong with how it is wired. It is acting like the generator is seeing a short. Check the wiring on the battery side of the ammeter for being shorted to ground and not going to battery. Otherwise, it seems like the regulator is not wired in properly. When the cut out pulls, you are getting full current to the field windings and the voltage is going to the moon, pinning the needle. Take another look and you might spot the problem. Eg. a frayed wire that might be touching ground, etc.

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Did change any wiring under the dash? It sounds like the wire going to the ammeter is hooked up backwards.

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Thanks everyone for the tips! The FLD and GEN terminals go straight to the generator and are brand new wires in an asphalt loom so I think that they are good. The BATT terminal has three items attached to it (under hood light, radio condenser, and ammeter) but these things are already grounded so would a ground short occur?

Anyway, I will start unwrapping the wiring this week and see what I find. I had to replace some of the wiring as it was 61 years old and crumbling. It might just be that I inadvertently connected something wrong on one of them. BTW, is there a way I can double check the battery gage beforehand? I didn't change any wiring under the dash as it's all intact but maybe the gage might be bad?

Thanks again for your time and help.

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Did change any wiring under the dash? It sounds like the wire going to the ammeter is hooked up backwards.

That would only cause the ammeter to read discharge when it is charging.

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The BATT terminal has three items attached to it (under hood light, radio condenser, and ammeter) but these things are already grounded so would a ground short occur?

I am not sure what you mean by these things are already grounded. Could you please explain.

As a test, disconnect the underhood light and the condenser from the regulator and try again.

Post back.

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You were reading my mind about disconnecting those two items. I will do it in the am and see what happens. What I meant about already grounded is the underhood light switch is grounded to the inside fender and the condenser is grounded to the firewall (both via simply being mounted to the frame. Bear with me if I sound uninformed as I am working on my first classic and have never been had much prior auto mechanic experience. I know that sounds like a dangerous game to be playing but it is what it is.

hpim0017.jpg

Edited by GaryP5
added picture (see edit history)

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The thing that causes the output of the generator to increase is an increase of the of the voltage/amperage to the field windings. Your most likely culprits are the regulator or the wires to the generator. You do have the fat wire connected to the gen terminal and the thinner wire to the field?...........Bob

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Ok, just wanted to make sure we were on the same page as to what you meant by grounded. Do you have a multimeter and know how to use it?

By the way, that old Pontiac is looking pretty good!!!

One nice thing to do would be to find a moulded upper radiator hose that fits...even if you have to cut it out a piece of a longer hose. It is just one of my hang-ups and I am a little coo-coo.

Also, make sure the paint is scratched off where you have that ground strap connected to the block.

Post back with your results.

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Thanks for the compliments, it's been a lot of work. I did some old aircraft restoration when I was in the Air Force but this is my first go with a car. I do have the wires connected between my gen and reg just as Bob asked. Second, this morning I removed the main ground strap plus the smaller engine to firewall strap and sanded both of their connection points plus the underlying block paint. Next I removed both wires connected to the gen and made sure they were the same as above. Fired it up to check the gage and no change. Lastly, I have a multimeter and am just learning to use it so I think I can figure out what you would be saying to do with it. One last thing... I used a hydrometer and checked the 6 volt battery cells and they were all good and fully charged. I think that is good, but is there a chance it could be over-charging?

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I is there a chance it could be over-charging?

Absolutely! If all of that current is going into the battery, it will boil it dry in no time.

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Hi there,i had a similar problem when i rewired a 37 cadillac,it acted like your car,had the generator rebuilt,a couple of regulators were tried to no avail,it drove me nuts for 2 summers,could not shut the car off anyplace as it did not have enough juice to start after running for a while,battery was slowly wearing down,the last time i had the regulator and generator set up,the mechanic gave me a little drawing as to how it should be hooked up,what i had was different then his drawing,all my charged up juice was going no place,i had to switch my load and feild wires,it was the wire from the generator had lots of current,just no place for it to go to?it was a couple of years ago and my memory isnt great,and i cant put it into words what i am getting at,i think if you understand what i am trying to say,you might try this in your next step?,i had lots of current,it wasnt getting to the battery like it was supposed to,i was lucky to find a mechanic that knew how to setup the old system for me,ever since then the car charges great and is reliable to boot.HTH Harvey B

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Thanks again for all your help guys. Here's my update. First I disconnected the condenser and underhood light connections from the regulator (no change).

Then after reading the service bulletin (THANKS!) I disconnected the field terminal while the engine was running (for fully charged w/ high charging rate). The ammeter did not drop off (no change to the acceleration/high charging swing). So from what I gather, and you already mentioned, I probably have a short in the generator or wiring harness somewhere. Again I'm on my third voltage regulator with the last one coming directly out of the box with no change to the gage so I'm going to rule it out for now. The wiring in my car is simple and least likely to be the cause (IMO) so I am going to pull the generator first and give it the once over. Anyone have any tips to ops checking it before I remove it? Maybe testing it with a multimeter?

stp64917.jpg

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Your field windings are shorted to ground internal of the generator. I had a 37 Plymouth that did this and the simple fix was to replace the generator. It would charge with the field wire disconnected and is not supposed to.

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That would make sense as I disconnected the FLD terminal from the regulator with the engine running and the gage still continued to swing to charge with acceleration. I would rather fix the generator than to buy a new one as they seem to be scarce. Would it be difficult to rebuild?

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Would it be difficult to rebuild?

No.

Check where the field terminal comes through the case. It might be shorted there... missing isolation grommet, terminal pushed over, etc.

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Well I'm pretty sure the generator is grounded internally. Earlier today I pulled the FLD wire off from the regulator with the car running and the gage did not drop off. Just now I pulled the FLD terminal directly off the generator with the car running and it still did not drop off so the ground should be in the generator and not the wiring harness... correct?

IaAlso pulled the inspection band off the gen and checked the internal terminal ends and wires with an inspection mirror and they all looked okay. Blew it out real good with a compressor and then checked the isolation grommets. One disintegrated so had to rebuild a new one but all of this didn't make a change to the gage reading so it looks like I'm in the market for a new generator.

I have a show this weekend so am not going to attempt to pull anything until Monday. I just searched through a GM parts interchange book and a Chevy gen will work for my Pontiac. Which is good because I haven't had much luck searching for one using my make yet.

Anyway... you've been a great help and have given me the courage to dig deeper than I did a couple of days ago. I appreciate it and will keep you updated once I get the new part installed. If you have any leads to help me find a new generator then that too would be appreciated. THANKS AGAIN!

~Gary

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I almost forgot. What did you mean by a new moulded upper radiator hose? Is it because of the style I am using or the size (somewhat too big)? I'm trying to keep the car as original looking as possible so feedback is appreciated.

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