The Ford Barn

Gold Digger · 02-09-2023, 09:18 PM

Just bought a new amp meter and replaced it with the wiring same as on the old amp guage but shows discharge. I switched poles with the wires and now shows charge. I had it wired exactly the way the books show the wiring diagram. Now it is the reverse but works right. Has anyone else had this problem?

TMarsh · 02-09-2023, 09:50 PM

Seems like I had the same issue. Just reversed sides and it worked OK. Probably just
Chinese repo.

rotorwrench · 02-10-2023, 08:21 AM

Connecting the amp meter is problematic in the way a lot of the diagrams were drawn. It's clear as mud on most of them.

Amp meters have a charge side and a discharge side. The terminals on the back correspond to charge and discharge. They aren't marked on the back so a person only needs to know the relationship between charge and discharge. Illustrations sometimes don't get the point across since the person interpreting the illustration can't tell which side the wire circuit is connected to. Is it the front or is it the back of the instrument?

The battery is the component that represents discharge since any current draw comes out of the battery. The generator represents charge since that is the component that charges the battery. This is how they should be connected.

WHN · 02-10-2023, 09:03 AM

Years ago I had the same issue. Did the same thing you did. Has now been working fine for over 20 years.

Enjoy.

fundytides · 02-10-2023, 09:09 AM

Common issue. Many ammeters seem to be designed for negative ground systems and since the Model A is normally positive ground, these ammeters must be hooked up "backwards" to properly reflect charge and discharge.

rotorwrench · 02-10-2023, 11:53 AM

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The ammeter used by Ford in the 6-volt positive ground era was designed to work with that polarity. If polarity is changed then the ammeter would have to follow suit. DC ammeters read the flow of current in or out from the battery so they are polarity sensitive.

The 6-volt converted alternators, usually the GM 10si, have an internal jumper to make them positive ground units. If a person goes 12-volt negative ground then the ammeter wires have to be reversed.

Later Fords with the inductive meters will require that the main power lead be reversed through the loop if polarity is changed.

02-09-2023, 09:18 PM	#1
Gold Digger Senior Member Join Date: Nov 2011 Location: Arkansas & Alaska Posts: 645	Amp. meter replacement Just bought a new amp meter and replaced it with the wiring same as on the old amp guage but shows discharge. I switched poles with the wires and now shows charge. I had it wired exactly the way the books show the wiring diagram. Now it is the reverse but works right. Has anyone else had this problem?

02-09-2023, 09:50 PM	#2
TMarsh Senior Member Join Date: Jun 2019 Posts: 131	Re: Amp. meter replacement Seems like I had the same issue. Just reversed sides and it worked OK. Probably just Chinese repo.

02-10-2023, 08:21 AM	#3
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: Amp. meter replacement Connecting the amp meter is problematic in the way a lot of the diagrams were drawn. It's clear as mud on most of them. Amp meters have a charge side and a discharge side. The terminals on the back correspond to charge and discharge. They aren't marked on the back so a person only needs to know the relationship between charge and discharge. Illustrations sometimes don't get the point across since the person interpreting the illustration can't tell which side the wire circuit is connected to. Is it the front or is it the back of the instrument? The battery is the component that represents discharge since any current draw comes out of the battery. The generator represents charge since that is the component that charges the battery. This is how they should be connected.

02-10-2023, 09:03 AM	#4
WHN Senior Member Join Date: Mar 2017 Location: Connecticut Shoreline Posts: 1,824	Re: Amp. meter replacement Years ago I had the same issue. Did the same thing you did. Has now been working fine for over 20 years. Enjoy.

02-10-2023, 09:09 AM	#5
fundytides Senior Member Join Date: Feb 2013 Location: New Brunswick, Canada Posts: 480	Re: Amp. meter replacement Common issue. Many ammeters seem to be designed for negative ground systems and since the Model A is normally positive ground, these ammeters must be hooked up "backwards" to properly reflect charge and discharge.

02-10-2023, 11:53 AM	#6
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: Amp. meter replacement Sponsored Links (Register now to hide all advertisements) The ammeter used by Ford in the 6-volt positive ground era was designed to work with that polarity. If polarity is changed then the ammeter would have to follow suit. DC ammeters read the flow of current in or out from the battery so they are polarity sensitive. The 6-volt converted alternators, usually the GM 10si, have an internal jumper to make them positive ground units. If a person goes 12-volt negative ground then the ammeter wires have to be reversed. Later Fords with the inductive meters will require that the main power lead be reversed through the loop if polarity is changed.