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Old 06-26-2018, 08:23 PM   #1
Mad Mac
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Default Reverse ammeter readings

I am useless with electrical issues, so I hope someone can diagnose this problem for me: When I turn the kill-switch on (with key out), the ammeter moves left (ie reads negative amps) but nothing on the car is turned on. Then when I insert the key and turn it on, the needle moves right (positive amps) still with nothing turned on except the key. I am sure this is not what is meant to happen - can anyone tell me whats going on?
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Old 06-27-2018, 05:21 AM   #2
Patrick L.
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Default Re: Reverse ammeter readings

I think we need a little more info.

To me it sounds right now as though there is a draw [ something is on that shouldn't be] somewhere and that the ammeter is wired backwards [ switch wires]. [ 2 issues]

Have you had this monster running to see what it does with the engine running at a fast idle ?
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Old 06-27-2018, 07:18 AM   #3
marty in Ohio
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Default Re: Reverse ammeter readings

Mad Mac,
Could it be that you have an ignition switch with an accessory terminal?
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Old 06-27-2018, 03:36 PM   #4
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Default Re: Reverse ammeter readings

Maybe I should explain better: My 1929 RPU is a regular runner and is normally quite reliable. It is absolutely stock standard and fully restored. A few days ago, I noticed the ammeter showing negative amps with the key off and positive amps with they key on, with all lights turned off. As that is exactly the opposite to what should happen, there must be an electrical problem. Since noticing it I have been reluctant to run the engine.

The ammeter is wired correctly, as I have been using the truck without any problems for years. Also, there is no accessory terminal as in post#2. I hope that makes the problem clearer.
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Old 06-27-2018, 03:48 PM   #5
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Default Re: Reverse ammeter readings

I would disconnect the headlight wire at the cutout And see if that does anything. If not try disconnecting one wire at a time at the junction box. Just try to isolate where the problem might be.
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Old 06-27-2018, 04:15 PM   #6
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Default Re: Reverse ammeter readings

My first thought was that maybe the cutout was stuck closed, causing the generator to attempt to 'motor' when the battery disconnect was switched on. The other details made me less sure.


I'd suggest to try what wmws suggested, but then carry it further and disconnect the wire from the cutout to the terminal box should the headlight wire or horn wires show no difference.
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Old 06-27-2018, 09:23 PM   #7
Tom Wesenberg
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Default Re: Reverse ammeter readings

This is what happens when you drive on the wrong side of the road. LOL


Engine off, but key on, and it shows a charge is what's puzzling.
I'd start the engine and see what happens.
Is this stock generator and cutout with + ground?
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Old 06-27-2018, 09:41 PM   #8
Mad Mac
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Red face Re: Reverse ammeter readings

Quote:
Originally Posted by Tom Wesenberg View Post
This is what happens when you drive on the wrong side of the road. LOL


Engine off, but key on, and it shows a charge is what's puzzling.
I'd start the engine and see what happens.
Is this stock generator and cutout with + ground?
Its a stock generator and cut-out but not sure whether its positive or negative ground (I don't even understand what that means).
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Old 06-28-2018, 01:12 AM   #9
cpf240
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Default Re: Reverse ammeter readings

Quote:
Originally Posted by Mad Mac View Post
Its a stock generator and cut-out but not sure whether its positive or negative ground (I don't even understand what that means).
How is the battery connected?

Stock Model A has the positive terminal connected to the frame and the negative terminal connected to the starter switch mounted on the starter.

The opposite of pretty much all cars today.

However, the A will work either way, with some noticeable differences, such as the ammeter reading backwards, unless it was hooked up backwards.
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Old 06-28-2018, 08:10 AM   #10
Tom Wesenberg
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Default Re: Reverse ammeter readings

The + post on the battery is larger than the - post. Be sure the + post goes to ground, then polarize the generator by using a short wire to touch between the 2 cutout terminals for 1 second. Then see how the ammeter acts.
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Old 06-28-2018, 08:31 AM   #11
Will N
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Default Re: Reverse ammeter readings

Are you sure you are turning the key on and off correctly? If the engine happened to have stopped at spot where the points were closed, when you turn on the kill switch and turn ON the ignition, you would expect to see a discharge on the ammeter. And if you then turned OFF the ignition, you'd see the ammeter move back to 0. The behavior you're describing sounds like you are turning on the ignition when you think you are turning it off, and vice versa.
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Old 06-28-2018, 11:34 AM   #12
Bob C
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Default Re: Reverse ammeter readings

Since you are not familiar with positive ground is there any chance you had a dead
battery and charged it backwards. Still not sure that would cause the problem you are having.


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Old 06-28-2018, 02:01 PM   #13
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Default Re: Reverse ammeter readings

Quote:
Originally Posted by Mad Mac View Post
Its a stock generator and cut-out but not sure whether its positive or negative ground (I don't even understand what that means).
"Ground" translates as "earth" in English-speaking countries - neither of which is a very good term. "Common" is a better term for vehicles and portable equipment, although it is hardly ever used. It refers to the polarity of the battery post that connects to the frame, which is the common connection for everything electrical in the car.

Used to drag a chain attached to the frame as a "safety" feature just to piss off the speed cops.
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