The Ford Barn

sethkestenbaum · 06-23-2022, 02:03 PM

My Ammeter was not going positive, so I decided I likely had a bad cut out. I replaced the cut out, polarized the generator (jumping the cut out for a second with the car running), and now I have a positive ammeter reading when in idle which DECREASES when I increase the throttle. It is the decrease that I am finding odd. What would cause a drop in the amperage? The only thing I can think of is a loose fan belt that slips at speed. Thoughts?

1955cj5 · 06-23-2022, 03:09 PM

Go through the same process but *without* the engine running.

With the engine running the cutout would be closed, completing the circuit, and jumping it would have no effect.

nkaminar · 06-23-2022, 04:20 PM

Measure the voltage at the battery. As the battery gets re charged after starting the car it is normal for the current to go down. Measuring the voltage will provide you with the data to see if this is the case.

rotorwrench · 06-24-2022, 07:52 AM

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The best way to polarize a 3-brush generator is to remove the brush cover and clip a jumper lead to the 3rd brush lead then momentarily touch the other end or the jumper to the battery negative terminal. This will magnetize the field pole shoes using the field coils and set polarity to positive ground.

If the generator had been working it should still have residual magnetism in the field coil pole shoes. Generators are somewhat sensitive to engine rpm but the amperage shouldn't increase very much. If it changes too much, the battery or other circuit wiring terminals may be loose or dirty. Make sure all connections are clean and tight.

06-23-2022, 02:03 PM	#1
sethkestenbaum Senior Member Join Date: Jun 2011 Location: Westchester County, NY Posts: 632	Odd Ammeter Reading My Ammeter was not going positive, so I decided I likely had a bad cut out. I replaced the cut out, polarized the generator (jumping the cut out for a second with the car running), and now I have a positive ammeter reading when in idle which DECREASES when I increase the throttle. It is the decrease that I am finding odd. What would cause a drop in the amperage? The only thing I can think of is a loose fan belt that slips at speed. Thoughts? __________________ Seth Kestenbaum www.oldcarroadtrip.com

06-23-2022, 03:09 PM	#2
1955cj5 Senior Member Join Date: Apr 2015 Location: Boise, Idaho Posts: 1,578	Re: Odd Ammeter Reading Go through the same process but without the engine running. With the engine running the cutout would be closed, completing the circuit, and jumping it would have no effect. __________________ Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62

06-23-2022, 04:20 PM	#3
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,898	Re: Odd Ammeter Reading Measure the voltage at the battery. As the battery gets re charged after starting the car it is normal for the current to go down. Measuring the voltage will provide you with the data to see if this is the case. __________________ 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.

06-24-2022, 07:52 AM	#4
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,422	Re: Odd Ammeter Reading Sponsored Links (Register now to hide all advertisements) The best way to polarize a 3-brush generator is to remove the brush cover and clip a jumper lead to the 3rd brush lead then momentarily touch the other end or the jumper to the battery negative terminal. This will magnetize the field pole shoes using the field coils and set polarity to positive ground. If the generator had been working it should still have residual magnetism in the field coil pole shoes. Generators are somewhat sensitive to engine rpm but the amperage shouldn't increase very much. If it changes too much, the battery or other circuit wiring terminals may be loose or dirty. Make sure all connections are clean and tight.