1957 Gen light dim at idle and gets brighter at higher RPMs

[57bowensbird]

I just recently had my generator rebuilt because I was having issues with it before, gen light would come on at high RPMs, but then started smoking after a drive.

After installing did a test drive and noticed that the gen light is very dim at idle but as the RPMs increase, the gen light gets brighter.

Also noticed that my headlights are not working anymore while the car is running or just off the battery.

Would love some input if anyone has any idea.

 

[Dick Rupp]

I just recently had my generator rebuilt because I was having issues with it before, gen light would come on at high RPMs, but then started smoking after a drive.

After installing did a test drive and noticed that the gen light is very dim at idle but as the RPMs increase, the gen light gets brighter.

Also noticed that my headlights are not working anymore while the car is running or just off the battery.

Would love some input if anyone has any idea.

Check the generator belt. Too loose and condition.

 

[Dick Rupp]

Check the generator belt. Too loose and condition.

Also check the voltage regulator

 

[57bowensbird]

Also check the voltage regulator

Belt is new, had to go with best fit one because mine has an aftermarket fan. It is a ribbed one if you think that may make a difference. But belt is tight, about half inch movement, and on correctly.

How would I check and test the voltage regulator?

 

[Ward 57]

I'll agree with Dick. Check your connections to the regulator. Something sounds like it's miss-wired. If the light gets brighter you know your generator is putting out current. Did you properly energize the field? You can't just hook it up, there is a process to get it working properly. Don't have it on hand at the moment.

 

[1957Bird]

Would ck with rebuilder to see if they polarized the gen on test stand or if you need to do it on the car. Assuming that you tagged your wires and have reinstalled properly.
as Ward has said, don’t have procedure at hand but pretty easily found.
good luck

 

[doug7740]

I'll agree with Dick. Check your connections to the regulator. Something sounds like it's miss-wired. If the light gets brighter you know your generator is putting out current. Did you properly energize the field? You can't just hook it up, there is a process to get it working properly. Don't have it on hand at the moment.

Polarization is a procedure which matches the polarity for the generator and the voltage regulator. The majority of Thunderbirds are manufactured negative ground, except for the 1955 Thunderbird which was manufactured positive ground. The generator has to be setup for either polarity. The generator will charge either way, however the voltage regulator has only one polarity. After the installation of a battery, generator or voltage regulator follow this procedure.

The terminals on the voltage regulator are labeled ARM, FLD and BAT, and this is where you will do the polarizing procedure. Both the generator and voltage regulator will have battery power, so don’t start the vehicle or turn the ignition on before polarizing them. You will need a small piece of 14 to 16 gauge wire for this procedure.

Before starting the car take the short jumper wire and briefly touch the FLD terminal to the BAT terminal to polarize the generator. You can touch the terminals a few times and it will produce a soft light spark. Under no circumstances touch the FLD terminal or any other part of the regulator or you could damage the regulator.

So you can double check the wiring at the voltage regulator, attached is a picture from the Thunderbird Restoration and Specifications Manual.

doug7740
1955 Thunderbird Blue

 

[57bowensbird]

Polarization is a procedure which matches the polarity for the generator and the voltage regulator. The majority of Thunderbirds are manufactured negative ground, except for the 1955 Thunderbird which was manufactured positive ground. The generator has to be setup for either polarity. The generator will charge either way, however the voltage regulator has only one polarity. After the installation of a battery, generator or voltage regulator follow this procedure.

The terminals on the voltage regulator are labeled ARM, FLD and BAT, and this is where you will do the polarizing procedure. Both the generator and voltage regulator will have battery power, so don’t start the vehicle or turn the ignition on before polarizing them. You will need a small piece of 14 to 16 gauge wire for this procedure.

Before starting the car take the short jumper wire and briefly touch the FLD terminal to the BAT terminal to polarize the generator. You can touch the terminals a few times and it will produce a soft light spark. Under no circumstances touch the FLD terminal or any other part of the regulator or you could damage the regulator.

So you can double check the wiring at the voltage regulator, attached is a picture from the Thunderbird Restoration and Specifications Manual.

doug7740
1955 Thunderbird Blue

Labeled the wired and installed the way the generator came out. Did not polarize the regulator before I started the car after I installed it. Would that cause issues? I did just polarize it now after learning I need to do that. Has not fixed the issue though.

 

[doug7740]

If the generator light stays on at full brilliance, you have no voltage at the voltage regulator terminal that goes to the armature. The armature is acting like a dead short and that causes the bulb to glow. This is why the idiot light is on before the engine is running. If it glows dimly or flickers, the voltage at the armature is low. Sometimes this is caused by low RPM. If the light goes out when you accelerate it could be normal or your voltage regulator might need adjustment.

The voltage at the regulator armature connection can be from 12.8 to 14.2 volts for a 12 volt system, depending on the regulator temperature. See the shop manual.

doug7740
1955 Thunderbird Blue

 

[57bowensbird]

If the generator light stays on at full brilliance, you have no voltage at the voltage regulator terminal that goes to the armature. The armature is acting like a dead short and that causes the bulb to glow. This is why the idiot light is on before the engine is running. If it glows dimly or flickers, the voltage at the armature is low. Sometimes this is caused by low RPM. If the light goes out when you accelerate it could be normal or your voltage regulator might need adjustment.

The voltage at the regulator armature connection can be from 12.8 to 14.2 volts for a 12 volt system, depending on the regulator temperature. See the shop manual.

doug7740
1955 Thunderbird Blue

I get that at idle the gen light will come on because the generator isn’t producing enough power. But my issue is that it is getting brighter with higher rpms.

 

[doug7740]

I get that at idle the gen light will come on because the generator isn’t producing enough power. But my issue is that it is getting brighter with higher rpms.

If the generator warning light is getting brighter with higher rpms, that tells me that you have no voltage at the voltage regulator terminal that goes to the armature. I think it’s time to evaluate your charging system.

Your charging system consists of the battery and cables, the generator and an external voltage regulator. The function of the battery is to spin the starter motor to start the engine. Once that’s done, the generator takes over, satisfying the car’s electrical demands and keeping the battery charged. The battery then acts primarily as a filter, keeping voltage spikes from damaging the car’s electronics. The voltage regulator rapidly switches the generator in and out of the charging circuit to provide the car with the correct voltage.

In 1955, the electrical system of the Thunderbird was 6 volt positive ground. In 1956, the Thunderbird electrical system was changed to 12 volt negative ground. On the 12 volt system there are two important numbers to remember, they are 12.6 volts and 13.5 volts.

12.6 Volts: If you think your car has a 12 volt battery, it doesn’t. The 12 volt battery actually has six individual 2.1 volt cells (one under each fill cap). Thus, when fully charged, the battery should have a resting voltage of 12.6 volts. If with the engine off, if the resting voltage is less than 12.6 volts, the battery is low and needs to be recharged. Of course it begs the question; why is the battery low? It could be that the generator isn’t working, or that the battery has reached the end of its useful life.

13.5 Volts: With the engine running the generator should output a charging voltage that’s about a volt higher than the resting voltage, or about 13.5 volts. The exact charging voltage may be as low as 13.2 volts or as high as 14.2 volts.

Take a multi-meter and set it to measure DC voltage, then measure the voltage across the positive and negative battery terminals with the engine off. As I said on a 12 volt system, a fully charged battery should read a resting voltage of 12.6 volts. After you start the car you should see a charging voltage of about a volt higher than resting voltage. If the reading doesn’t increase by about a volt or if it stays at the resting voltage, it means that the generator isn’t recharging the battery. This could be because the generator is defective, the regulator is defective, or the wiring between them has failed.

A basic charging system health test: Use a multi-meter to measure the resting and charging voltages as described above. Then with the engine running gradually increase the electrical load by turning on the headlights and the blower fan. Then increase the engine RPM to about 2,500 as you watch the reading on the multi-meter. If the voltage stays about a volt higher than resting voltage, then the car’s charging system is functioning. But if the voltage drops or increases dramatically at any point, there’s a problem with the generator or the voltage regulator.

doug7740
1955 Thunderbird Blue

 

[BudP]

Thank you Doug7740 for sharing your knowledge and experience. Your explanation and exposition of the 12 volt charging system will be printed and inserted into my technical reference book for my 1957 T-Bird (which my grandson has already asked for!).

 

[Ward 57]

Thank you Doug7740 for sharing your knowledge and experience. Your explanation and exposition of the 12 volt charging system will be printed and inserted into my technical reference book for my 1957 T-Bird (which my grandson has already asked for!).

LOL. Grandson eying your hobby toy? Make sure he is involved in everything you do. The logic involved in diagnosing the problem, to the geometry of the linkages, to fluid flows of the cooling system. What a learning experience that will carry over when he goes on in his life and being a 'handyman'. My wife married me because I can fix almost anything. Plus I can cook, another life skill that should not be ignored.

 

[Pink T-Bird]

Need to re-open this thread.
Since I've had the car my gen light was on very dimly at all speeds at night with the headlights on, possibly a bit brighter at higher engine speeds, but just slightly. I don't drive the car at night often so I was going to address it "some day".
Well, after the Veterans Day parade this week I now have @57bowensbird 's problem. The light is on dimly at idle during the day, and light gets brigher with engine speed, going to full brightness at about 1800 rpm. The prior owner has an aftermarket ammeter installed and it agrees - shows discharge, a constant negative amp draw. I have my dad's old contact ammeter and it shows 50 amps from the generator so must be the regulator? Swapped in an old 30A Fomoco script regulator that had tested good when it went on the shelf many years ago (10 or more). Same issue. So I pirated a 35A regulator off a '58 Edsel Citation and issue cured! But 35A is too much for the 30A generator so I can't leave it in, plus the Edsel needs it back. The light out at all engine speeds and ammeter shows charging.
I've looked at the regulator test and adjustment procedures in the shop manual, and they are honestly beyond my capability. The only old time auto electrical shop I knew of closed at the start of the pandemic. Anyone have a shop they recommend I can send these 2 original fomoco 30A regulators to for adjustment? looking at several T-bird catalogs no one has an OEM authentic looking new replacement, so I want to get these repaired.

 

[paul5456]

Since the regulators are usually all the same size, you can replace the non-stock looking cover with your old cover. Check with whomever you are buying from if this is possible.

 

[74 Harley]

@Pink T-Bird , you could leave the 35 amp regulator on. It means that regulator can handle up to 35 amps. Won't hurt or damage the 30 amp generator.
I don't know of anyone rebuilding vintage regulators at this time. Good luck.

 

[Ward 57]

Since the regulators are usually all the same size, you can replace the non-stock looking cover with your old cover. Check with whomever you are buying from if this is possible.

I replaced my regulator years ago and unfortunately disposed of my old one. It was Ford blue and looked out of place. Recently I took the cover off, painted it gloss black and put on the decal that is available from CASCO. Looks totally correct now.