The Ford Barn

31blackcoupe · 12-08-2023, 05:45 PM

Okay, i'm totally frustrated. thanks for any help. My '29 all of a sudden ate the battery. Ok got a new one . Somehow it was hooked up as negative ground when I bought it. Ran fine until the battery died. Hooked up the new battery as negative ground and no lights! Replaced the cut out with a negative ground and still no lights. Gen spins by itself clockwise. Tried a positive ground cut out, still no lights. Disconnected cut out with negative ground and lights work. I swear it was negative ground when I got it. If I leave it on negative ground the battery eats itself up. Completely gone next day. I've tried both negative and positive ground cut outs, still no slights. Engine will run.Do I need a new generator?
Any suggestions appreciated.
Thanks,
art
.

nkaminar · 12-08-2023, 06:32 PM

Does the battery go dead when the engine is not running, i.e. the car is parked? Or does it happen when you are driving the car? 12 volt or 6 volt?

Remove the cutout. Run the engine at a fast idle and measure the voltage at the generator. If you have a 6 volt system the generator should be putting out about 10 volts or higher. Do not run the engine for long or you may burn out the generator. If the generator is not putting out any voltage you may need a new one, or if you are handy with electrical systems you may be able to find the fault in the generator by taking it apart and using your multimeter.

If the generator is putting out 10 volts or higher (with a 6 volt system) then put the cutout back but leave the wire that goes to the lights disconnected. Run the engine at a fast idle and measure the voltage at the cutout or at the large cable that attaches to the starter switch. It should be about 7 volts. If the voltage is close to zero then you may have a bad cutout or there may be a bad short somewhere. Disconnect everything except the battery and ignition and try again. If the voltage is good you have a short somewhere.

If you are getting good generator output then measure the resistance to ground for the wire that goes to the light switch with the lights out and with the lights on. The resistance should not be close to zero (about 0.5 ohms). If it is close to zero then you have a short in your wiring for the lights.

Do all the above and then report back what you found. There may be some other problems but this will get you started chasing down the reason your battery goes dead.

Added: If the battery goes dead while the car is parked then you have drain somewhere, like a short or the dash light left on. Check the dash light first, but if that is not the cause then look for shorts or perhaps the brake light switch being stuck on (look at the brake light). Start by disconnecting everything. Then use your multimeter in the resistance setting to see if there is a drain to ground in any of the circuits. There should be infinite resistance in any circuit if the circuits are off, such as the lights or ignition switch.

eagle · 12-08-2023, 08:04 PM

Look at the coil, one side of the primary terminals should have + or - by it. See which side goes to the distributor. If it is - to distributor then its negative ground, if its + going to distributor, it's positive ground. Another way is look at the ammeter when cranking, should dip negative when the points close, if it goes positive then you've got the polarity reversed

jrelliott · 12-09-2023, 11:39 AM

If it is not a diode cutout, then the cutout is not polarity sensitive. There is really a relay inside the cutout. The coil for this relay is attached to the generator side of the cutout. When the voltage from the generator is sufficient the coil is energized and makes the connection from the generator to the battery connection on the cutout. If your cutout is bad, the connection from the generator to the battery is always made and would try to motor the generator thus discharging the battery. Your generator will work either negative or positive ground depending on how you polarize the generator. To check the cutout disconnect the battery, light and horn wire from the cutout and measure the resistance from the battery terminal on the cutout to the generator terminal. You can also see if the coil of the relay inside the cutout is working as should be a small amount of resistance from the generator terminal , with the generator output disconnected from the cutout.
I would check the cutout, and if it is good, repolarize the generator to either positive or negative ground, depending on the polarity you have chosen. Start up the vehicle and check the voltage at the generator output at the cutout and the battery output of the cutout. If you have voltage at the battery output of the cutout, then things should work.

Joe K · 12-09-2023, 05:29 PM

Quote:

Remove the cutout. Run the engine at a fast idle and measure the voltage at the generator. If you have a 6 volt system the generator should be putting out about 10 volts or higher.

Not to critique, but the Model A generator will "peak out" about 32 volts when not restrained by a load. This is why many are able to use the Model A generator against a 12V battery, especially with the right voltage regulator.

Now amperage is another matter. Most of the reason for upgrade to a "real" 12V generator is found in the "augmentations" frequently used alongside - like modern headlights.

Still, that 32V is worth keeping in mind - not the least of which it can kill you.

Joe K

rotorwrench · 12-10-2023, 01:52 PM

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The only component of an OEM model A electrical system that deals with voltage is the battery. The 3 or 5 brush generators put out current depending on how the field brush is adjusted. I use positive ground since that is the way it was designed to work. The diode for a cut out is OK but the actual cut out relay is my preference. I set the field brush for 5 amps at idle using an original ammeter. The repro ammeters are not up to my standards.

I would go all 12-volt negative ground if I wanted to go that route. Use a modified GM 10si alternator for charging and higher current function. It's the simplest way to go 12-volt. Change all the bulbs and either ballast the coil or use a 3 Ohm primary type coil.

12-08-2023, 05:45 PM	#1
31blackcoupe Senior Member Join Date: Oct 2014 Location: Elgin, IL Posts: 115	"29 electrical/generator failure Okay, i'm totally frustrated. thanks for any help. My '29 all of a sudden ate the battery. Ok got a new one . Somehow it was hooked up as negative ground when I bought it. Ran fine until the battery died. Hooked up the new battery as negative ground and no lights! Replaced the cut out with a negative ground and still no lights. Gen spins by itself clockwise. Tried a positive ground cut out, still no lights. Disconnected cut out with negative ground and lights work. I swear it was negative ground when I got it. If I leave it on negative ground the battery eats itself up. Completely gone next day. I've tried both negative and positive ground cut outs, still no slights. Engine will run.Do I need a new generator? Any suggestions appreciated. Thanks, art .

12-08-2023, 06:32 PM	#2
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,897	Re: "29 electrical/generator failure Does the battery go dead when the engine is not running, i.e. the car is parked? Or does it happen when you are driving the car? 12 volt or 6 volt? Remove the cutout. Run the engine at a fast idle and measure the voltage at the generator. If you have a 6 volt system the generator should be putting out about 10 volts or higher. Do not run the engine for long or you may burn out the generator. If the generator is not putting out any voltage you may need a new one, or if you are handy with electrical systems you may be able to find the fault in the generator by taking it apart and using your multimeter. If the generator is putting out 10 volts or higher (with a 6 volt system) then put the cutout back but leave the wire that goes to the lights disconnected. Run the engine at a fast idle and measure the voltage at the cutout or at the large cable that attaches to the starter switch. It should be about 7 volts. If the voltage is close to zero then you may have a bad cutout or there may be a bad short somewhere. Disconnect everything except the battery and ignition and try again. If the voltage is good you have a short somewhere. If you are getting good generator output then measure the resistance to ground for the wire that goes to the light switch with the lights out and with the lights on. The resistance should not be close to zero (about 0.5 ohms). If it is close to zero then you have a short in your wiring for the lights. Do all the above and then report back what you found. There may be some other problems but this will get you started chasing down the reason your battery goes dead. Added: If the battery goes dead while the car is parked then you have drain somewhere, like a short or the dash light left on. Check the dash light first, but if that is not the cause then look for shorts or perhaps the brake light switch being stuck on (look at the brake light). Start by disconnecting everything. Then use your multimeter in the resistance setting to see if there is a drain to ground in any of the circuits. There should be infinite resistance in any circuit if the circuits are off, such as the lights or ignition switch. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 12-09-2023 at 08:08 AM.

12-08-2023, 08:04 PM	#3
eagle Senior Member Join Date: Aug 2011 Location: Eagle Bend, MN Posts: 2,025	Re: "29 electrical/generator failure Look at the coil, one side of the primary terminals should have + or - by it. See which side goes to the distributor. If it is - to distributor then its negative ground, if its + going to distributor, it's positive ground. Another way is look at the ammeter when cranking, should dip negative when the points close, if it goes positive then you've got the polarity reversed __________________ "There are some that can destroy an anvil with a teaspoon and shouldn't be allowed to touch anything resembling a tool."

12-09-2023, 11:39 AM	#4
jrelliott Senior Member Join Date: May 2010 Location: Pine, AZ Posts: 794	Re: "29 electrical/generator failure If it is not a diode cutout, then the cutout is not polarity sensitive. There is really a relay inside the cutout. The coil for this relay is attached to the generator side of the cutout. When the voltage from the generator is sufficient the coil is energized and makes the connection from the generator to the battery connection on the cutout. If your cutout is bad, the connection from the generator to the battery is always made and would try to motor the generator thus discharging the battery. Your generator will work either negative or positive ground depending on how you polarize the generator. To check the cutout disconnect the battery, light and horn wire from the cutout and measure the resistance from the battery terminal on the cutout to the generator terminal. You can also see if the coil of the relay inside the cutout is working as should be a small amount of resistance from the generator terminal , with the generator output disconnected from the cutout. I would check the cutout, and if it is good, repolarize the generator to either positive or negative ground, depending on the polarity you have chosen. Start up the vehicle and check the voltage at the generator output at the cutout and the battery output of the cutout. If you have voltage at the battery output of the cutout, then things should work.

12-10-2023, 01:52 PM	#6
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: "29 electrical/generator failure Sponsored Links (Register now to hide all advertisements) The only component of an OEM model A electrical system that deals with voltage is the battery. The 3 or 5 brush generators put out current depending on how the field brush is adjusted. I use positive ground since that is the way it was designed to work. The diode for a cut out is OK but the actual cut out relay is my preference. I set the field brush for 5 amps at idle using an original ammeter. The repro ammeters are not up to my standards. I would go all 12-volt negative ground if I wanted to go that route. Use a modified GM 10si alternator for charging and higher current function. It's the simplest way to go 12-volt. Change all the bulbs and either ballast the coil or use a 3 Ohm primary type coil. Last edited by rotorwrench; 12-10-2023 at 02:17 PM.